In time, however, remove the cardboard from the jar. Low and behold, the fleas, trying to avoid the pain associated with jumping, will now jump only high enough to avoid hitting the piece of cardboard, which remember, is now no longer in place.
Do you allow people to put a "lid" on you? Maybe you are the one moving the lid in place. Reflect on whether or not you find yourself no longer "jumping high," because you are afraid of the anticipated pain.