One thing that often disrupts momentum and really shouldn't is competitors.
A board member of mine used to say sales fix everything in a startup, and that is really true.
Wait to start a startup until you come up with an idea that you feel compelled to explore.
At the beginning, you should only hire when you have a desperate need to.
Employees will only add more value over time.
One of the great and terrible things about starting a start up is that you get no credit for trying.