OOOOR ... people with low mood tend to be less able to engage in activities?

It reminds me of that joke: a biology professor is teaching physiology. He takes a frog and says "jump". The frog jumps. The prof then chops the frog's legs, and says "jump" again. The frog now stands motionless. "We conclude", says the prof, "that a frog's hearing depends on its legs!".