Question: You walk down a path through the woods everyday. You always walk by one particular large rotting log which weighs over a ton. The next day you notice that there is another large log underneath the familiar one that you've never seen before. How did it get there?
Answer: The path is through a valley and near a stream. By chance a flood washed the log underneath.
Question: A semi truck weighing exactly 10,000 pounds gets onto a bridge that is 100 miles long. The bridge's weight limit is exactly 10,000 pounds, any more will break the bridge. After going about 80 miles down the bridge a small bird lands on the truck.
Answer: Nothing, after traveling 80 miles the truck will have surely burnt enough fuel to allow the bird to land on the truck without breaking the bridge.