Suppose you came across a waterfall where the water was briskly cold and it was super hot outside. You'd find a way to get under it. At first it would be exhilarating in a too-cold sort of way but then you'd get tough and adjust. Beyond that you'd grow comfortable in the cool cool water.
Meanwhile, in the shower, it's nearly impossible to drag the knob all the way to cool unless dared by a spouse.
Which brings me to my pointa-obscura.
Single speeds are the chilly waterfall. You can go way cooler than you otherwise will because there's no control knob allowing you to meter your pain. The result is that you push through and become stronger & faster. Either that or you don't go in the water at all.