[Alex/Mugaaz]

When he doesn't raise he "loses" by not taking your money with his equity edge preflop. I.E. He loses by not taking as much from other people, him not raising only increases other's wins because their losses will be less.

He also loses if him not raising gives someone odds (implied or not) to draw out on him. In this case his mistake his giving those players that much in gain, depending on what their odds are.