It is as if, in math, you had to concern yourself with your posture at the table, and with how you are holding the pencil, and with how beautifully you are writing the symbols that go into that next equation and whether it is centered on its line. In math, if you need twenty minutes to decide what your next step must be, you take twenty minutes. But you cannot delay for twenty minutes as you figure out which foot to move next or which way to turn your head. A musician must control the body as well as the mind, to be sure, but the control of the body doesn't go into nearly as much detail. You cannot ignore posture ever when you dance.
Bodies are like that.
But it is enjoyable, too, and in my experience the harder you work the more fun you have. The pleasure and satisfaction that you derive from learning even the simplest step make up abundantly for all the work, and every new step mastered brings a new delight. For me, in fact, the enjoyment has always been the main consideration and the healthy exercise only secondary. If it were more generally known how it feels to take ballet classes, the studios would be packed and there would be waiting lists to get in. It can also induce a wonderful peace of mind.