Clearly I can't speak for the OP but I'll give my answer: common sense.

There are many rules that infrequent fliers might not be aware of and generally I would argue that it's their job to be informed before flying. But this rule, that the over head bin above your seat doesn't belong to you (and your seatmates), defies logic so I can understand why it is a source of confusion for many.

Of course the space above your seat should be reserved for you and your seatmates (or I would argue the space directly across, but I digress). To be made to place your bag 20 rows away makes it impossible to monitor it during the flight to protect yourself from theft. It makes deplaning much harder for everyone because there are those who have to swim upstream to collect their bags. If the carry on baggage rules were enforced, no one would have to worry about their bag not fitting in the bin above them. It is a terrible injustice that a person carrying a "legal" bag can be forced to check it simply because some imbecile was allowed to bring on everything but the kitchen sink.

And the cretins who would drop their bag at row 10 when they are seated in row 30 should have their bag taken down and checked immediately. No questions, no hesitations. If this was airline policy people would stop engaging in this selfish behavior. And that policy, along with enforcing the written carry on rules, would eliminate the overhead bin wars and enable passengers to place their bag where it should be...in the bin right over their seat.