The fable of The Wild Boar and The Fox - Fables of Aesop
A WILD BOAR was whetting his tusks against a tree, when a Fox coming by, asked him why he did so; for, said he, I see no reason for it; there is neither hunter nor hound in sight, nor any other danger that I can see, at hand.True, replied the Boar; but when danger does arise, I shall have something else to do than to sharpen my weapons.
Moral:
It is too late to whet the sword when the trumpet sounds to draw it.
