War Nerd (Gary Brecher), in RPG vs. M1, draws an analogy between tanks and knights:
Fact is, no tank in the world is totally invulnerable to RPGs, any more than any knight was totally invulnerable to arrows.If you think of a tank as an internal-combustion knight, you get a better sense of how it’s meant to work. The armor is concentrated up front, so the knight/tank can attack without having to hold back. The idea is that he has to be able to shrug off what they throw at him while he’s spurring the warhorse full-speed over the battlefield — then hit hard.
If he’s unhorsed — if the tank is forced to stop and deal with lots of dismounted enemy — then it’s all over. It’s as easy as knifing a turtle