Sometimes I'm the shark; sometimes I'm the swimmer.
You can play the game with one person and one character and there is an extra card that is suggested you get for that purpose so you have some chance.
I have also played the game with four characters and just me. I loved that experience but it was a lot to manage. You could also play with two people and two characters, etc. From what I saw in the kick starter preview game I was sent, it is totally flexible in that way.
The "Grit" card is there for playing a single character. If you watch the videos you will see that the enemies (maybe other things as well) scale based on the character count so you can do whatever you want.