Some people put a lid on their potential.

Fleas can jump extremely high. In fact, a flea can jump over 150 times its own height. In an experiment, a scientist placed a number of fleas in a glass jar. They quickly jumped out. He then put the fleas back into the jar and placed a glass lid over the top. The fleas began jumping and hitting the glass lid, falling back down into the jar. After a while, the fleas, conditioned to the presence of the glass lid, began jumping slightly below the glass lid so as not to hit it. Basically, they got smart. They realised that there was no point knocking their heads against the lid. In fact, they got too smart for their own good. They became conditioned to jump a ‘safe’ height. When the lid was removed, the fleas continued to jump at a ‘safe’ height. Essentially, they accepted the limit imposed on them and thereby imposed it on themselves. They were conditioned to remain trapped in the jar forever!