If you're a writer, it happens to you. Some plot issue weighs on your mind. Perhaps it's a relationship you need to complicate, a character you want to eliminate in a memorable fashion or an event you want to foreshadow in a clever manner. You think about even when you don't know you are. Then out of the blue, the solution strikes you like a lightning bolt. You know it will work.
The only bad thing about ideas slapping your overburdened minds during those times is the difficulty of writing it down before you forget it. I usually try to work out the details surrounding the lightning bolt so I don't forget the main part. I've forgotten a few times like the time I got the tractor stuck in a wet part of the yard.
I know some people get those flashes of inspiration as they fall asleep or dream about them. They keep a notepad by the bed so they can write them down. I almost never think of anything useful for my writing before I fall asleep since it usually takes me about forty seconds to drift into mindless slumber.
What about you? When do those lightning bolts strike you? Do you ever forget them before you can write them down?