During a research experiment, a marine biologist placed a shark in a large holding tank and then released several small bait fish into the tank. As expected, the shark quickly swam around the tank, attacking and eating the smaller fish.
The marine biologist inserted a clear fiberglass divider into the tank, creating two separate partitions. She placed the shark on one side of the fiberglass and a new set of bait fish on the other.
Once more, the shark swiftly attacked. However, this time, the shark rammed into the fiberglass barrier and rebounded off. Undeterred, the shark kept attacking every few minutes with no success. Meanwhile, the bait fish swam around unharmed in the second partition. Eventually, about an hour into the experiment, the shark gave up.
Over several weeks, the experiment was repeated multiple times. With each iteration, the shark’s aggression gradually diminished. It learned that its attempts to reach the bait fish on the other side of the divider were futile. Eventually, the shark ceased its futile efforts altogether, resigning itself to the perceived barrier.
Then marine biologist then removed the fiberglass divider, but the shark didn’t attack this time. The shark had been conditioned to believe a barrier existed between it and the bait fish, so the bait fish swam freely, unharmed.