It’s very common among autistic people and neurodivergent people in general, it’s called executive dysfunction. Essentially your brain has trouble both making and initiating plans. Every time I brush my teeth I have to remember to do it (this is not automatic, all my toothbrush stuff is set up as a visual cue any time I’m near the sink), focus on my task as I go to the bathroom so I don’t forget why I went there, remember to take my medicine first so that I don’t have to swallow them after brushing my teeth, floss, and brush.
The last two parts sound very simple (and they are, which is why this is so frustrating for many people), but sometimes I will stand in front of the bathroom sink for 5 or 10 minutes, knowing I need to brush my teeth, WANTING to brush my teeth, but it’s like whatever ‘go juice’ neurotypical people have a limitless supply of is just limited for me. Finally after standing there and psyching myself up I can do it, but it does take legitimate effort to initiate the process even if I follow through on all the parts smoothly. I couldn’t tell you exactly why this happens even though I can obviously recognize that it is happening, I kind of suspect it has to do with wonky sensory integration problems (common in ADHD and autistic people).