What stops an innovator from filing his intellectual property?

How many of you have a good idea, something you think is going to go far, but then do nothing about it?
What is the difference between the entrepreneur who takes the idea and turns it to cash, and the creative individual who does not?

I ponder this given I find myself in the latter position all too frequently. Admittedly it is difficult in my current role as inevitably the client owns the IP, whether it was their idea or not, when the thought is performed in their cheque book time, they own it. The other disadvantage that I see is that I signed a contract when starting with my current employer that said they basically own my ideas. It would be an interesting challenge and in hindsight it was not something I should have signed. Think about it, there is a clause in a contract that states any independent though, no matter when it was made or how it was arrived at, is owned by your employer.

That aside, I would doubt they would get in the way of progress, more likely profit would run both ways.
But this brings me back to my original thought - what stops us from taking the idea and turning it into intellectual property. Here's a list of hurdles I perceive (initially assumptions), and will over the next few posts figure out how to break down.

1. Lawyers are expensive, I'll obviously need one to file my patent.
2. Will someone find it valuable, if they do then how can I prevent them from just taking the idea - I'll be needing my expensive lawyers again to content infringement.
3. Seems like a lot of work writing a patent - I don't even know the process for filing.

I'm off to do my research now.