I tend to follow well-trodden paths. My mind is not often on what I'm actually doing so it's better to be a creature of habit. In daily life my last big "aha" had to do with shopping. You know those wine bags stores give out if you buy six bottles - they give from ten to thirty percent off? I have four or five of them. One day I did't have enough bags for the groceries. The only one left was a wine bag. But I wasn't buying wine. Suddenly it came to me. Other things besideds wine will fit in the wine slots!!! I put in a quart of milk, a jar of olive oil, celery: oh, the store was full of things that I could carry in a wine bag!
Pretty lame, right?
While writing, I'm used to plots twisting away from the plan and characters taking control of their own lives. But I usually know who dunnit and why. But there was one book... I was almost at the end and the murderer wouldn't confess. I begged and pleaded and offered him a dramatic speach but nothing worked. Finally he looked at me in disgust and said, "I didn't do it; he did." I looked at the other guy and realized that he had indeed been guilty. And, when I reread the book, the clues were all there.
Sometimes one has to give oneself a good shake and be prepared to be surprised.