A liar will not be believed, even when telling the truth.
There was a Shepherd Boy who tended his sheep at the foot of a mountain near a dark forest. It was lonely for him, so he devised a plan to get a little company. He rushed down towards the village calling out “Wolf, Wolf,” and the villagers came out to meet him. This pleased the boy so much that a few days after he tried the same trick, and again the villagers came to his help. Shortly after this a Wolf actually did come out from the forest. The boy cried out “Wolf, Wolf,” still louder than before. But this time the villagers, who had been fooled twice before, thought the boy was again lying, and nobody came to his aid. So the Wolf made a good meal off the boy’s flock.
Townsend version (The Shepherd’s Boy and The Wolf)
A shepherd-boy, who watched a flock of sheep near a village, brought out the villagers three or four times by crying out, “Wolf! Wolf!” and when his neighbors came to help him, laughed at them for their pains. The Wolf, however, did truly come at last. The Shepherd-boy, now really alarmed, shouted in an agony of terror: “Pray, do come and help me; the Wolf is killing the sheep”; but no one paid any heed to his cries, nor rendered any assistance. The Wolf, having no cause of fear, at his leisure lacerated or destroyed the whole flock.
There is no believing a liar, even when he speaks the truth.
L’Estrange version (A Boy and False Alarums)
A shepherd boy had gotten a roguy trick of crying (a wolfe, a wolfe) when there was no such matter, and fooling the country people with false alarums. He had been at this sport so many times in jest, that they would not believe him at last when he was in earnest: and so the wolves brake in upon the flock, and worry’d the sheep at pleasure.
He must be a very wise man that knows the true bounds and measures of fooling, with a respect to time, place, matters, persons, Etc. But religion, bus’ness and cares of consequence must be excepted out of that sort of liberty.