My body is filled with healthy, vibrant energy.

Bodies respond to being used more reliably than to being spared. A day spent carefully conserving energy often ends with less of it than a day that included a cold walk nobody wanted to take.

That is a genuinely strange piece of arithmetic, and it holds for most people most of the time. The tank fills by being drawn on.

It has limits. Real exhaustion is not solved by a brisk walk, and pretending otherwise helps nobody. But somewhere below that point there is a wide territory where the smallest possible amount of movement returns more than it takes.