"Stepwilk: Since I have never flown aircraft long and powerful enough to whack their tails, can somebody explain to me what causes tailstrikes?"
Actually, if you are around small tricycle planes, especially those used for training or rental, take a look at their tail tiedowns. You will note that a lot of these have flattened bottoms, the result of inadvertently becoming tailskids multiple times through tailstrike incidents. In training they most commonly happen when practicing low-speed liftoffs into ground-effect (short or soft-field techniques).
So length and power don't necessarily have a lot to do with it. It is a question of either poor control technique, or correct technique applied at too low a speed.
Put simply, if the aircraft will suffer a tailstrike at, say, 12 degrees, then the rotation (even if perfectly executed) had better not take place until the speed (and thus lift) is sufficient to lift off at a lower angle of attack (say, 8 degrees).
While small planes usually rotate and lift off at "oh, about 65 knots," a specific Vr is calculated for every heavy-aircraft flight based on weight, air temp, etc. Either a poor calculation of Vr, or an error in setting that Vr on the airspeed gauge, may lead the pilot to rotate at too low a speed. Flying by the numbers only works if the numbers are right.