system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What happens in our brain, when we forget what we wanted to do while starting to do the action?
gpt
Our brain reinforces pathways we take more than once.  Often what happens when we forget what we wanted to do while starting to do something is that a more reinforced brain pathway is triggered when we start the action, causing us to forget the rest once it leaves short term memory.

Sort of like the challenge of patting your head while rubbing your stomach.