If you only have a hammer, you tend to see every problem as a nail.
Abraham Maslow

Bad company is like a nail driven into a post, which, after the first and second blow, may be drawn out with little difficulty; but being once driven up to the head, the pincers cannot take hold to draw it out, but which can only be done by the destruction of the wood.
Augustine of Hippo

There are horrible people who, instead of solving a problem, tangle it up and make it harder to solve for anyone who wants to deal with it. Whoever does not know how to hit the nail on the head should be asked not to hit it at all.
Friedrich Nietzsche

A nail is driven out by another nail. Habit is overcome by habit.
Desiderius Erasmus