What stops a start-up?

Earlier this week I was talking to someone about starting up in business / working for themselves. This girl would be great, she is passionate about what she does; is a real expert in her field; she’s a great communicator / personality, and clients would love her.
But she’s holding back, perhaps not confident that it’ll work.
It got me to thinking – what stops a start-up?
For some it will be the loss of security of income. It can be tough when you’ve got a mortgage and a young family to give up a salary to chase the dream.
For others it can be a lack of confidence.
For many it is a lack of funding, and in this present financial climate, an inability to raise the capital required.
And for some it’s simply down to a lack of knowledge about how to go about working for themselves.
In these tough times of austerity and government spending reviews, one thing is certain. Hundreds of thousands of people are going to find themselves out of work. For some this will present an ideal opportunity to take the plunge and go for it.
So what do we need to do to encourage and support these entrepreneurs?