Bread gained by deceit is sweet to a man,
but afterward his mouth will be full of gravel.
Consider the gravel. There is the gravel of a painful conscience. What at the moment seemed to be exciting comes back to haunt the heart that is not given fully to wickedness. The transgressor worries about breaking God's law and its consequences. If he is not too far gone, he is troubled by the wrong has done against his neighbor.
There is the gravel of consequences. Even if his conscience does not bother him, he now must deal with the trouble of keeping up his deception. If he is found out, he must take the trouble of avoiding capture or avoiding conviction. He must take caution to protect himself from retribution. He may avoid legal prosecution, but then must suffer the loss of his reputation. His neighbors do not trust him nor respect him. He himself is now avoided.
And then he may well find that the bread he stole is not what he thought it would be. It actually is not satisfying; it does not accomplish for him what he thought it would. He finds that his eyes and reasoning had deceived him.
What is the bread you desire? A good career? Wealth? Good looks? Break the law of God in obtaining them and you will find their sweet taste turn to gravel in your mouth.