How many triangular chevrons, and how many of the other round pieces do players have access to in a 2-player game?
For Pacru you need the following
2 players 4 chevrons (triangular) 42 markers (round)
3 players 3 chevrons 28 markers
4 players 3 chevrons 24 markers
In Pacru the figure for markers is limited as once you've got that many on the board, you've won.
Note that for Azacru & Shacru the number of markers can be larger - you are provided with 50 in the standard 302 set but you'd be unlikely to get up to that many on the board, even in a 2 player game.
Rules are on the Pacru website in PDF format.