Why Do We Forget What We Were Supposed To Do The Minute We Enter A Room?

Psychologists believe that walking through a door and entering another room creates a mental blockage in the brain, meaning that walking through open doors resets memory to make room for a new episode to emerge. 

This is generally referred to as the doorway effect.

Human memories are episodic, as opposed to clear, linear narratives, which means that they are segmented and strongly depend on the person who makes them. 

For example, the way one remembers a particular incident will most likely differ from the way another person remembers exactly the same incident.