When you're have a small company you're hoping to turn into a larger one, many deadlines are every bit as existential as a DoD proposal deadline for a defense contractor. Especially when you don't have a big slosh pool of VC funding (but this is largely true even if you do), the difference between "stable and growing at a healthy pace" and "if something doesn't change we'll have to shut down" is often one or two customers.
This is only a feasible plan for people without any children or committed relationships though. Telling your spouse that you'll skip the vacation because work is more important than them will not go over well, for obvious reasons.
Right, in that case, I'd probably give up my vacation instead.