The bear lost his tail because he was tricked by a fox. The fox told the bear to put his tail in the hole in the ice to catch fish, but when the ice froze, the bear's tail got stuck and broke off.
The bear lost his tail because of his own gullibility. The fox deceived him into thinking he could catch fish with his tail in the ice. Unfortunately, the bear didn't realize it was a trap and ended up losing his tail when the ice froze around it.
Well, it happened like this. The bear was a bit naive and believed the fox's suggestion. When he put his tail in the ice hole, the cold made the ice solidify and trap his tail. When he tried to pull it out, his tail broke off.