How would you know your generated idea is valid?

By testing the idea. There are many ways to test your idea, and of course the ways you choose are determined by the idea you've generated. Mainly there are three root tests. Those are: is there a substitute for your idea? if so, is your idea better in anyhow than those substitutes?. Does your idea solve a problem? if so how does it solve the problem. Finally and most importantly, Does your idea fulfill or create a need?By answering those questions, you'll know whether your idea is valid and valued or not.After that, if it is valid you can apply your idea in the real life.