A lot of game design is winning mental battles with yourself. Your brain is a sneaky beast that tries to sabotage you in one of two ways. Either "This game is horrible, your playtesters are bored, it'll never succeed and you should drop the project" or "This game is wonderful, anyone who says otherwise can't see your vision, ignore feedback and release it immediately!" Unfortunately there's no simple trick to overcoming it, since these situations require opposite responses.
With no simple recourse the battle comes down to being able to tell how closely your thoughts mirror reality and (when they inevitably don't) in what direction they're inaccurate. There are a few options in the designer's toolkit to help achieve this.
The first is the Swiss army knife of game design: Playtesting. Your opinion of your game is compromised so being able to get honest feedback from an outside perspective is helpful in correcting your own view. It is a little more complicated when it comes to deciding whether to continue with a work in progress since what you're assessing is "What will this game be like when it's done? Is that good enough to justify continuing to pour time into it?" and as an expert your predictions for how it will develop are probably more accurate than the average playtester. There's also an issue of taste in that you need to obtain feedback from someone who will like the type of game that you're creating - finding that someone doesn't like a genre does nothing to help you clarify your view. Still, despite its limitations, playtesting remains the strongest tool at your disposal.
The second is a greater understanding of how and why your brain lies to you. If you're under the impression that you have perfect self insight and that what you perceive always maps on to reality: Dissuade yourself of this notion now. Look at some optical illusions and observe that even when you know what's really there you can't make your eyes see them. Take an implicit association test and observe that even though you think everyone should shoulder their fair share of the work your millisecond response rate is faster when women are paired with housework rather than careers. What you are (whatever you are, you weird meat imprisoned thought construct) is not the same as your brain - the thing that you perceive as "you" is constantly mislead and misdirected by what you've probably got used to thinking of as 'your' brain.
However the understanding that your brain lies to you gives you tools. You can read about the various cognitive bias that most people experience. While you can't become immune to them (There's a cognitive bias describing the bias that people who learn about cognitive biases have that makes them believe that they have overcome them - which is wonderful) you can start to recognise when they apply. If you've been working on something for a long time then you can recognise that you might be invested in it and manually adjust your opinion - recognising that you're likely to be thinking of it as more successful than it is and dropping the project if it's borderline.
The third thing that you can use is your own decision about how you would like to fail. Ultimately any course of action is a risk: If you abandon a project then it might be that you've discarded something that could have been amazing. If you continue with one you might waste your time and eventually produce something that any thinking person would be ashamed to have created. Neither of these are desirable outcomes, but making a concious choice about what sort of error you'd rather make and biasing your decisions in those directions can help you to make tough decisions where all other factors seem balanced.
Beyond the mental battle necessary to put in the hours necessary to bring a good game to life while also taking steps to kill ideas (or parts of ideas) that you love, there's another layer to the conflict in how it's influenced by external forces. Game design is something of a social endeavour, you wind up interacting with a lot of different groups: Playtesters, peers, players, publishers, people who write reviews and other things beginning with "P". They all have opinions, they're all going to give them (with various levels of diplomacy) and whether you like it or not it'll affect your mood and therefore your ability to think clearly about the games that you're creating.
Here are some things that have been written to me or about my games this month:
"I must be a needle in a haystack of messages but you were always very responsive"
"[8.5] A very good co-op game, with more going on than the likes of Pandemic..."
"...the last log was a month ago. Reading the comments section is increasing my concern..."
"Sorry to be a pest, but wanted to keep you updated..."
"I would like to state that Greg is a pro! He replied fast and solved the problem with super professionalism."
"[1.0] This game has the honour of being the worst that I have encountered. I would rather watch Space Jam whilst listening to the Frozen soundtrack, than take part in this game."
"I can't say I'm not disappointed..."
"OK now Im starting to get really mad, numerous times I was lied to and now I even sent a invoice last week to be refunded and I am being blown off AGAIN!"
"Thanks again for the upgrade."
"My thanks go out to everyone involved in making that happen. It was far more than I expected."
All of this had some sort of an impact. I find it easier to put a lot of energy into creating, playtesting and developing games when faced with evidence that it was worth the trouble last time and that my goal - fundamentally to make people happy - is achievable in this way. I find it tougher to solve problems when attempts to make things better for people are met with hostility. Those seem pretty natural responses, I'm sure most designers share them and "messages from gamers" represent only a fraction of the necessary communication to do the job well.
I think that most designers are motivated by the same thing and will experience a similar mental battle here. Taking everything too personally will quickly undermine your ability to work, since the negative seems to stick better (I've seen this comment on more than a few fellow designer's blogs). No matter how well things go, there will always be *some* negative somewhere - some human beings will be awful to you no matter what you do. Conversely, not taking things personally at all stunts growth. Sometimes someone is mad because they have a right to be and your mistake made that happen. There's an extent to which that deserves to be taken seriously rather than shut out because it's unpleasant to think about.
This creates another layer to the mental battle necessary to design games effectively, but again, one that can be managed. Giving each piece of feedback as much time as the others so as not to disproportionately weigh the negative stuff helps. Being aware of the level of problems with past projects that ultimately turned out well helps. Generally looking after yourself goes a long way to insulating your design work from shocks coming through from outside forces.
That's most of what I wanted to say, to try to describe the sort of mental struggle that goes on in designing games, so you could stop reading here. This is the end of the article proper, but if you're curious about why I decided to think about this topic and scribble some thoughts:
I have a charming little theory about the world which I refer to as "Everyone is screaming on the inside."
Essentially it holds that mental disorders of various stripes and colours are dramatically more common than some of our most dismal predictions. Most people have something serious going on, but are pretty much able to give the impression of functioning to the outside world. People who appear to be fine outnumber people who do not appear to be fine. People who aren't fine outnumber people who are genuinely okay.
I have no idea if this theory is actually true, it probably isn't since it's based entirely on anecdotal evidence and such ideas tend to be nonsense. "Idea" is probably a better word than "theory" here. Still, anecdotally, I've never found a population in which it's applied so widely as it has to game designers. Particularly in the UK design scene (or at least designers who visit UK conventions) clinical depression seems mindbogglingly common. More than half of designers I've come across either are dealing with or have dealt with it (not that it ever goes away properly but you know what I mean).
Depression's not really a topic I can do justice to in a paragraph. I probably couldn't in a whole book. Also anything I wrote on the topic would be so fantastically generalised as to have at least one reader come back with "How dare you encourage people to think of it that way!" I guess if I'm going to write anything it'd be this: If you've not had experience of it and come across someone who has, listen more than you speak. Also if you have a simple and obvious idea that will help, it won't.
So I got into thinking about the sorts of mental pressures that exist in game design. Whether they're the sort that would cause these sorts of problem or if they're of the sort that people who've overcome that sort of problem would be better at dealing with them. That lead me into thinking about refinements to the process or tools that'd make them easier to deal with. It seems like an area that could use some thought.
Besides the benefits for game designers themselves - we're probably missing out on a whole boatload of awesome games that someone didn't make because they tricked themselves into thinking they weren't good enough