For the #mechanically#disinclined -- #seatbelts lock, mechanically, based on the amount of force you put on them. I know of (multiple!) people who have issues with this, because they are violently grabbing the seatbelt to put it on quickly (thus locking the seatbelt). Pulling it harder just locks it more. The trick is to SLOWLY and SMOOTHLY pull the seatbelt out and then secure yourself. No, there's nothing wrong with the seatbelt... it's their seatbelt technique.
