Working in security and doing security door/door access installs with a locksmith and getting into locksport, I've noticed- and maybe it's just a thing local to me- that like 95% of the doors in the world are not installed correctly. Holy shit you guys.
the worst i've seen was a new subdivision where all the french doors were installed over a couple of days. they sent an junior person to do it. all were installed upside down, which made them non-functional. they had to redo all the doors (probably not much better but at least right side up).