Momma Told Bud, When A Door Closes, Another Always Open. How Did Bud Understand This When He Was A Small Boy?

From the text:

She was also wrong when she thought I'd understand that nonsense about doors closing and opening all by themselves. Back then it really scared me because I couldn't see what one door closing had to do with another one opening unless there was a ghost involved. All her talk made me start jamming a chair up against my closet door at night.