It sounds like a pretty simple statement at first glance, but I believe there is a depth of truth to it beyond the obvious.
Human memory is a tricky and incredibly complex thing, and here is not the space to go into scientific detail, but we can discuss lived experience of how memories seem to work. In general, unless you have certain neurological conditions, we tend not to remember every single detail of every single day. There are parts that we only retain in the short term while we’re doing them or a little while after, and parts that may get grouped together as routines because we do the same things regularly – and sometimes you get a sense of operating on auto-pilot because those actions are so familiar you can do them unconsciously.