1. Not hiring well enough.

2. Not trusting those they hire.

3. Not expanding their skills beyond pitching their idea.

4. Not managing the basics.

5. Not stretching their comfort zone.

6. Not outsourcing.7. Not managing the BOD. 

Keep your eye on the ball,
Your head above the clouds,
Your ear to the ground, 
Your shoulder to the wheel,
Your nose to the grindstone,
Your finger on the pulse,
Your feet on the ground, and
Your head on your shoulders.
Now... try to get something done.

Source is my rant on 11 reasons why starting a company is hard:

http://ifindkarma.wordpress.com/2011/06/20/11-reasons-why-starting-a-company-is-hard/