I would say cash flow and the balance of winning / starting the next job. Meaning the urge is always there to start the next job , however you start to become stretched too thin. In theory, if you do great work, your reputation will carry you far as far as winning new clients etc. ONce you get there with your reputation, you can reach a point where you can charge a premium, and stay on one job until completion, then take on the next one . People will wait for quality work !
If you have a crew working for you , keeping your high quality of expectations will be an obstacle as well.