Ideas.. where do they come from? Life. It's that simple. Life is filled with people who don't know what the hell they are doing. There are those who THINK they know what they are doing and try to control the ones they think who don't know what they are doing, but in fact no one really knows what they are doing.
See? Where did that paragraph come from? Where did that come from? A moment in time. We are only a moment in time. And so is an idea. Catch them. Grow them. Write them down.
I find that once you have one idea, another appears and then another, and another, rather like drawing a tree, with each branch and leaf being a part of the whole, and in the end you have... a tree!... no, well, yes, but if we think about the written word, a book.