Personal emotions and business don't work well together. They are great to sell an idea but the same person shouldn't be in charge of actually executing it because they will still do it even when everybody else tells them it's crap.
I had to experience it and I think it's actually one of the greatest dangers in startups.
There are two sides to that idea, though. You can make incremental improvements through data and metrics and objective thinking, but no amount of selective user testing of incremental improvements would have, say, created the iPhone and subsequently turned Apple from an almost fallen star into the biggest company in the world.
I had to experience it and I think it's actually one of the greatest dangers in startups.