I didn’t realize that this was a thing until someone smarter than me posted a cartoon about it on Facebook (it’s good for something!). I always assumed it was further evidence of age related cognitive decline or evidence of a mind preoccupied with too many things at once. I feel better already.

The doorway effect is a known psychological event, where a person’s memory declines when passing through a doorway moving from one location to another, when it would not if they had remained in the same place. People experience this effect by forgetting what they were going to do, thinking about, or planning upon entering a different room. This is thought to be due to the change in one’s physical environment, which is used to distinguish boundaries between remembered events: memories of events encountered in the present environment are more accessible than those beyond it.
Wikipedia