I'll tell you how later

It always cracks me up. You sit down on the airplane and just before they close the door the captain turns on the fasten seat belt sign. Usually the flight attendants tell you that everyone must have their seat belt on before the plane leaves the gate. OK, so far so good, but if that is the case, why do they wait 5 to 15 minutes to tell us HOW to use the seat belts? It must be an FAA regulation. In the unlikely event of a fire on the airplane, while it is still at the gate, well before the safety demonstration, you will have to figure out how to unbuckle the seat belt you already put on all by yourself :)