I find that happens periodically with many things. Generally it means you are becoming more confident in what you are doing, which means you tend to either relax and cut a few corners, or get a bit adventurous and try new things. So you learn from your mistakes, go back to having some great results, which prompts you to become a touch overconfident again. It’s an ongoing cycle that continues for as long as you are open to learning new things (although the mistakes tend to get less horrendous as you gain experience).