You have to think and act like an entrepreneur.

Starting a company is tough.  It takes lots of hard thinking, lots of busy-work, and lots of time.  It's not a 9-to-5 job, and it will be taxing on your marriage and family life, if you have one.  You will be thinking about the job almost 24/7.  And you will absolutely love it, which enables and justifies this commitment.  Now, if this description doesn't fit you, then you probably aren't a 100% entrepreneur.  Sure, you can put your toe in the water and be half-committed, and maybe you'll be successful (or ride on the coattails of others who are committed), but most companies these days don't succeed with a part-time effort, and if you're the only one who isn't committed, then your job is in jeopardy.  No easy ride.  Feel free to reply with any stories or insights you have on this topic.