There is no great theory or mystery behind shifting. When Applying a force to the lever you are engaging a mechanical system, your force will be transfered the point of least resistance usually moving the Drum transferring to the next gear, but If for some reason it wont shift, that energy has to go somewhere usually a bent or broken shift fork. So basically on the gas, off the gas, clutch, or no clutch. If you have to push down or up with more than moderate force damage may occur. Thats about the size of it. Micro sprint racers weld their clutches solid and shift many many times with the clutch being totally non-existent and they dont experience any more transmisson damage than we clutch type have due to shifting. Now they have been known to destroy gears! but they are pushing crazy horsepower numbers at 10,000 + RPM the whole race. Thats another story!