【挑战极限第五季】挑战极限，你能跳得更高

Flea trainers have observed a predictable and strange habit of fleas while training them. Fleas are trained by putting them in a cardboard box with a top on it. The fleas will jump up and hit the top of the cardboard box over and over and over again.
Note
flea n. 跳蚤    cardboard n. 纸板
　　As you watch them jump and hit the lid, something very interesting becomes obvious. The fleas continue to jump, but they are no longer jumping high enough to hit the top. Apparently, Excedrin headache 1738 forces them to limit the height of their jump.

　　When you take off the lid, the fleas continue to jump, but they will not jump out of the box. They won't jump out because they can't jump out. Why? The reason is simple. They have conditioned themselves to jump just so high.

　　Once they have conditioned themselves to jump just so high, that's all they can do!

　　Many times, people do the same thing. They restrict themselves and never reach their potential. Just like the fleas, they fail to jump higher, thinking they are doing all they can do.
Note
restrict v. 限制、约束　　potential n. 潜能、潜力
　　中文：

　　跳蚤训练人在训练跳蚤时发现跳蚤有一个奇怪的习惯。若把跳蚤放在一个有顶盖的盒子里，他们会不断地跳起来，撞击顶盖。

　　你观察他们跳起来撞击顶盖，会慢慢发现一个有趣的现象。他们仍会跳起来，但不会再撞到顶盖。

　　当你把顶盖拿开时，跳蚤还会接着跳，但却不会跳出盒子。为什么呢？原因很简单。它们已经习惯了只跳那么高。

　　一旦它们习惯只跳这么高之后，它们就只能跳这么高了。

　　很多时候，人们也是一样。他们自己限制了自己，从来不去发掘自己的潜力。就像跳蚤一样，没能跳得更高，还以为已经到了自己能力的极限。