Can you compress a liquid, No. The gears "propell you forward" beacuse they mesh with eachother transferring tq through a number of gears of diffrent sizes causing a "reduction", the shift forks move the collars over the syncros meshing them changing to another gear set. Like any fluid an excess of heat breaks down the fluid until it becomes thin causing gears to graze eachother, also driver error has to do with it, you cant tell me you have never accidently grinded a gear shifting it happens, i have. Im not doubting your intellegence just clarifying things.