Did it decline when exercised, diminish when allowed a free course, one might let it alone, even encourage it, in order that it might the sooner be dead.

But, unfortunately, it works the other way.

The more one worries the more he continues to worry.

The more he yields to it the greater becomes its power.

It is a species of hypnotism: once allow it to control, each new exercise diminishes the victim's power of resistance.
Never was monster more cruel, more relentless, more certain to hang on to the bitter end than worry.