Everyone in the group project thinks they did most of the work. Do the math and it adds to 300 percent.

You have full access to your own effort and only partial access to everyone else’s. You remember every hour you put in, including the invisible ones, while their contributions appear to you only as finished results. That asymmetry is enough to make honest people all sincerely believe they carried the thing.

Assume you are inside that distortion rather than outside it. Ask what the others actually did, including the parts you never saw, before deciding you were the one holding it together. It also helps to say out loud what you contributed, since nobody else can see your hours either.