Well it's not really a "good" thing of course - it would be more convenient for ourselves if we could remember everything.
But yes it's normal to not remember all or even most of the code you write, there's just to much of it. Some people remember better, and it'll get a bit easier if you've seen more code, but in general you can't remember everything.
Which means that writing clear code and leaving comments is not just for your colleagues, it's also for your future self!