If you think of
1) the bike and rider remaining at a fixed height
2) the 'road' moving up and down under each wheel
Then the suspension is simply controlling what the wheels do - trying to keep them in contanct with the road most if not all of the time...
Too little compression damping and the wheels when the road moves up will keep the wheels moving up even when the road moves down.
Too much rebound damping will have the wheels leave the road when the road moves down ...
View this way the damping is effected by the spring strength and the weight of teh wheel togther with anything attached (brakes, swing arm, etc).
This is a simplistic view .. does not deal with too little rebound or too much compression. But it gives you an idea of what goes on..