David addressed this question in one of his psalms: "I have seen the wicked in great power and spreading himself like a native green tree" (Psalm 37:35). He also observed: "For I was envious of the boastful, when I saw the prosperity of the wicked. For there are no pangs in their death, but their strength is firm. They are not in trouble as other men, nor are they plagued like other men.... When I thought how to understand this, it was too painful for me--until I went into the sanctuary of God; then I understood their end. Surely You set them in slippery places; You cast them down to destruction" (Psalm 73:3-5, 16-18).
God permits a period when the wicked have the chance to repent. God's patience is meant to lead them to repentance (see Romans 2:5-7). But instead, they often presume on God and say, "He does not know what we are doing. We are getting away with it." And this seems to be true, for a time. But they will spend eternity in hell. Eternity is so long, and life is so short!
It is often true, too, that their own evil catches up with them. There is a statement in the common parlance, "What goes around comes around." If you deal out evil to people, it will come back to you.
Can you imagine anything more horrible than the latter years of a Mafia don, waiting for someone to do to him what he has done to someone else: Always in fear for his life, always in torment that someone will hurt him, just as he has hurt other people? Not having anyone to trust or count on; not knowing when the assassin's bullet is going to come?
This is true of so many of the wicked. They will usually be punished on earth while they live, even if it is not obvious to the rest of us. It may be nervous problems, or disease, or a child who disgraces them, or a wife who torments them. Rest assured, no one gets away with evil. Judgment always comes. Only the timing is uncertain.