Boredom was the biggest thing for me at my startup. When waiting around for the business guys to make the right partnership for 3 months while you refactor for a demo for the nth time....
That doesn't sound like a typical startup experience though. Typically it's the opposite: too many things to do and the deadlines are always too short.
I’ve lived this a couple times. I hate to be pessimistic, but it’s a really bad sign. The startups I’ve done that were successful were always running just at the edge of total meltdown because the business guys were hustling hard.