[iAinsley]

1) Yes, someone has already thought of your idea. It doesn't mean they plan on executing on the idea. It's the execution, not the idea that matters. It's execution that defines success.

2) Having a partner/co-founder or someone you can bounce ideas off of (besides your bias girlfriend) provides impetus and motivation for someone consumed with the day-to-day of living. If you're having a problem prioritizing your idea along with all of the gotta-eat stuff, then bringing someone in to bounce ideas off of is essential because time is literally fleeting and non replenish-able.

3) Engage other people. Most ideas fail in just this way, because the founder is afraid to share the idea with others. Thinking that person will run off with the idea. The odds of this happening are slim. Most people operate more ethically than that.

[gfodor]

"It's the execution, not the idea that matters"

This oft-cited bromide is a huge pet peeve of mine. The truth is, some ideas are much better than others. If you have a really good idea, often the ship will right itself on its own no matter how badly you execute. Your worst fear in those cases are other competitors beating you to the market, not your inability to draw customers.

[marknutter]

I think you're not getting why people say the execution is more important. First off, how do you know an idea is so great until it's become a huge success? Secondly, I run into people all the time who have "great ideas" but no technical expertise to pull it off, and they always believe that coming up with the idea is half the battle. Often times, the best ideas are the most obvious ideas, and of course the most obvious ideas are the ones most likely to have been thought of already. What sets people apart is their execution.

A ton of effort on a half baked idea is always worth more than no effort on a great idea, IMHO.

[vpdn]

This is only true if you have

a) a cure for cancer b) a solution for world peace

For any other idea, there's execution.