I like to think of it as having low RAM (and sometimes a random program/thought has a memory leak). It's not that someone just fully and completely forgets they put their food in the (muted) microwave, it's that the task is no longer running because they had to pick up the loaf of bread that fell on the floor or maybe their ponytail needs fixing. There's not enough RAM to run Eat Microwaved Food AND Fix Ponytail. With Fix Ponytail running and ending there's enough RAM to run something else but it has to be manually initiated.