Quirky family traditions

In our family, the youngest family member present always had to cut the cake on birthdays—even if they couldn’t even hold a knife yet. The explanation was: “Otherwise, the cake won’t grow properly.” Of course, no one ever questioned it until a two-year-old nephew once sawed right across the cake.

Even stranger: After every vacation, the car had to be completely emptied at home before anyone was allowed into the house. Apparently, this was so “the trip would be properly concluded.” Do you also have such fixed routines whose origins no one remembers anymore?

At our house, after spending a night away, nobody was allowed to make the bed until the window had been opened briefly. “Otherwise, the stranger’s sleep stays in the room” — sounds pretty esoteric today, but it was an ironclad rule. And when packing a suitcase, one item of clothing always had to be left out until the very end so that we would “surely come back.” No idea whether that was tradition or simply self-deception caused by forgetfulness.

I know the thing about completely emptying the car in a similar form: after long drives, we had to open all the doors once before turning off the engine. Supposedly “to air it out,” even though we were usually traveling in winter. Has anyone here ever actually figured out the origin of a rule like that?