I remember as my understanding deepened in chess I would get over-confident playing my friends, often losing silly games simply because I wouldn't look over the board or I would miss their ideas. I played happily assuming that my position had to be superior simply because I was the better player.
When I started analyzing my games I began to see certain areas where I was consistently misjudging positions. Whether it was the potential for a piece, a square, the danger I was in, or the positional superiority I had. I found I had chess blindspots. In most cases, for me, it's a matter of overlooking tactical themes.
But sometimes, I look back on a game and I simply can't explain why I didn't see something. In over the board games this is inevitable (at least for a player of my strength, or lack thereof). But in correspondence chess, it becomes frustrating because I do generally take my time looking over a position. I use the "Sit on your hands" method of analyzing a position. I take note of what my intuition tells me and then I challenge myself to find a better move than the "intuitive move".
I recently played a game with a good friend of mine from chess.com. I was reminded yet again of just how often my blindspots creep up in games, and how sometimes I have to sit on my hands until circulation has stopped and my hands are turning blue. It was a very fun, and for me, an interesting game. Of course filled with mistakes, but there was a lot going on in it. In hindsight, many of the ideas available in the game seem plain as day. But during the game, it felt every move was a difficult puzzle, and the game easily could have gone either way.