On the marvelously curious subreddit /r/DiWHY, redditor /u/carrieminaj asks why this door is shaped this way. One potential answer lies beneath the fold.
Redditor /u/ngpropman thinks that the extra vertical height is to allow the passage of mobile whiteboards or blackboards.
The setting looks like a classroom, conference room, or some other space where people gather together to communicate. Still, one must ask why it would not have been cheaper to assemble the whiteboards inside and accept the loss of their mobility.
Other redditors suggest that the gap space is to permit people wearing very tall hats to enter and leave easily.
-via Core77
One of my daughters thought of the correct solution immediately: because they had a door shaped like this, so they had to build a matching doorway.
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Digging for gems in the comments.
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