It's the DOOR

This explains a lot!
Ever walk into a room with some purpose in mind, only to
completely forget what that purpose was? Turns out, doors
themselves, are to blame for these strange memory lapses.
Psychologists at the University of Notre Dame have discovered
that passing through a doorway triggers what's known as an
"event boundary disparity syndrome" in the mind, separating one
set of thoughts and memories -- "gangliopsychdissynchronitis" --
from the next. Your brain files away the thoughts you had in the
previous room and prepares a blank slate for the new locale.

Thank goodness for studies like this. It's not our age,
it's that damn door!