If I were to pick a concept least likely to be accepted by my twelve year old denoting the difference between adults and children, it would be our attitude toward stuff. Children are natural hoarders. Legos, bits of a broken Happy Meal TM Incredibles toy, and the corner piece of what could be a Harry Potter puzzle; all are sacrosanct. All must remain, residing rent free in whatever corner of a toy chest or basket will have them.
I’ve noted that with age the gifts - birthday, Christmas, Father’s Day, etc. - I receive tend toward the perishable.