Well, it depends on the idea. If it's something that would help you personally then go ahead and do it anyway. Even if the startup fails you'll have built a product that can help you. If you are trying to solve a problem that a bunch of other people have then you should also do it, but make sure you find one or two of the people that would actually use your product and get feedback from them.

There is little reason to not just go ahead and do it. Either way you'll learn something and it should be a rewarding experience.