A good analogy is stretching a rubber band. You can stretch and stretch and even feel the tension increase in the muscles in your hands and arms as the gap from one end of the band to the other widens. But at some point you reach the limits of elasticity of the band and it snaps. The same thing happens with human systems.
I didn't actually realise what apartheid meant. I'm probably a bit naive, but I thought it was more of a vague segregation, like on the beaches and buses.