This is one of my personal faves, not very long, but the meaning is quite clear:
The Fox And The Scorpion
One warm, summers day, a lone fox makes his way along the banks of a river. He sniffed at the water lapping the edges of the river, wondering where the best place to cross would be? As he walked, he spotted a scorpion sitting in the grass, but continued to walk, paying it no attention.
The scorpion walked through the grass and cut the fox off, standing in his way, its pincers clasping at thin air, its tail held high above its head, the stinger dripping beads of venom onto the ground. The fox regarded the scorpion for a moment, before asking,
"May I help you?",
The scorpion pointed at the water with one of its pincers and replied,
"I too need to cross the water!",
The fox watched the scorpion warilly, he did not trust it,
"I'm afraid, I can not help you!", the fox told the scorpion,
"Bend down, let me climb on your back, you can swim across carrying me!", the scorpion responded,
"If I let you climb on my back", the fox argued, "you will sting me, and I will drown and die!",
"If I do that!", the scorpion retorted, "I will drown and die too!".
The fox considered this, looking at the river, it was very wide, and very deep! Finally decided the scorpion was right, if he did sting the fox, he too would die! So the fox bend low on his front legs and allowed the scorpion to climb up, onto his back.
The river was not moving quickly, and before long, the fox had reached the centre, when he felt something sharp pierce the skin on his back, the scorpion had stung him! His legs began to slow, he could not make them move anymore, his tail went limp, and his entire body began to sink, under the water. Before the fox and scorpion completely disappeared into the blue, the fox asked the scorpion,
"Why did you do that?, now you will drown and die too!!",
the scorpion responded,
"I can't help it, it's in my nature!"