Years of study and what was the most useful thing I learned in film school? The dolley counter zoom? No. The Kuleshov Effect? No. How to overexpose film stock to create pseudo-solarization? No.
Before leaving a location you’ve filmed at, you look around one last time. Just to check that you’re not leaving anything behind. Just to be sure. It’s called the “idiot check”.
Every time I leave a hotel room, I make one last “idiot check”. It has always served me well.