For those of you who know me, this is an issue close to my heart. I'll be brief.
By far, the single thing most budding "entrepreneurs" lack is encouragement. It is unfortunately that simple.
Most people will tell you it's networking, or having capital, or a business plan, or even luck. All of those things are Step 2. Step 1 is starting, it is the point most people don't get past.
Novels 3/4 done; "great idea for a movie" that never makes it to script; business idea that never makes it past the cocktail napkin.
And all of that, in my experience, is not fear of failure but fear of the unknown. It is identical to the "cold approach" in dating. You're not afraid she'll mace you, you're afraid she'll ask you to sit with her and then you won't have anything to sustain the conversation.
"Will the world discover I'm a fraud?"
There is so much self-doubt and a lack of self-confidence. There are a myriad of reasons, summarized under the umbrella "we were taught to pursue security, not happiness."
No amount of startup capital can fix this problem. You will make poor decisions, you will stop short, you will be tentative, you will be nervous with the money. The problem is you, not the system.
As time and generations pass, we don't learn to deal with failure, we are taught to avoid failure. Instead of sending the kids outside to play and teaching them how to be safe around sticks/bullies/heights, it's easier to leave them in the playroom.
The solution, therefore, is to fail. A lot. And as fast as possible, as young as possible. If you're <25 go hit on ten women a night, cold, and get shot down. Feel what it's like. It's not _so_ bad, is it? Better than wondering.
Forget about finishing your novel. Put up the first five chapters on a blog. Force yourself to read the comments.
Think you're a filmmaker? Put up ten photos-- still pics-- on Flickr. And invite the hate. See if you really have an eye for this. If you don't, now you are free to try something else.
Etc.
At best, they may love you and there's your encouragement. Or maybe someone sees your work and a collaboration is born.
At worst, they hate you, and you realize you're still ok, you didn't run uptown for heroin.
Either way, the failure will hold your hand and walk you to success.