Though the cat were possessed of nine lives, worry would surely kill them all--either one by one, by its horrid and determined persistence; or all at once, by the concentrated virulence of its power.
There are many proverbs to the effect that "When worry comes in, wit flies out," and these are all true.

Worry unsettles the mind, unbalances the judgment, induces fever of the intellect, which renders calm, cool weighing of matters impossible.

No man of great achievements ever worried during his period of greatness.

Had he done so his greatness could never have been achieved.

Imagine a general trying to solve the vexing problems of a great combat which is going against him, with his mind beset by numberless worries.