Disclosure: not a neuroscientist just an enthusiast. Please correct where I’m wrong.

The nervous system is running an incredible amount of processes at the same time, the vast majority of which you’re not aware of. Our awareness is a tiny sliver. What may seem like a mistake to you may be a statistically insignificant lapse considering all the computations going on.

Why the mistakes for shit you know how to do? Hard question. One reason may be that you’re not experiencing life in real time. Everything that happens takes a bit of time to get perceived, processed, and synthesized into meaningful information. If you waited for that entire process to happen before reacting, you’d be at a disadvantage. So the brain literally simulates reality, it forms expectations on past experiences and lessons, and it predicts what happens next. That’s why you can catch a ball, and why it takes time to learn how to catch a ball. Your brain predicts where the ball will be and you place your hand there in anticipation. If you had to actually analyze all of the information all the time, you wouldn’t be able to get anything done. My understanding is that the brain doesn’t have the compute power to do everything in real time, so it has to automate a bunch of things. When it does that, sometimes it makes mistakes, or sometimes reality throws a curve ball and the prediction was incorrect.

Lastly, forgetting is a feature, not a bug. Can you imagine never forgetting anything, ever? You would be inundated with memories you would have to triage. Ideally you remember shit that matters, the rest is a waste. Repetition shows that something is important and worth remembering.