I don't know if this is common among software engineers, but occasionally I will look back over some code that I wrote myself a few months prior and it won't be immediately obvious what's going on. I know that somewhere in my head I understand it very well–I figured out the problem, wrote it, wrote tests (probably), and I was able to explain it during review if challenged. But in that moment, it was like I'd never seen it before.
Early in my career I had to occasionally write C#; building UI with razor was pretty common then before there were any workable front end JavaScript frameworks. I was stuck on a problem so turned to Stack Overflow. I found a question that matched my issue, and scrolled to an answer that was clear and held the solution. Then I looked at the author of the answer. It was me, a year earlier.