You TDD your goals. Square could certainly have started with modest goals, like we did with Basecamp, such as "get to $4K/month in revenues". That probably wouldn't have floated for them, given all the VC they took. But there are many grays between that and "unseat every POS ever".
Well I guess you could say that you could split the goals to things like "make a prototype", "convince some VCs", raise "$100,000", etc. That makes for bitable chunks, but the goal has to remain. Otherwise, what's the point of breaking one's ass for 4000$/month?