Slackness Vs. Persistence

The Flowers Of Guidance Volume One Preventing Negligence
If humans carry out all actions with persistence, we are sure to succeed. Endeavor and enthusiasm alone can create delight and merriment. Here we can see passengers of Apollo 11 happy and joyful, as they are about to travel to the Moon.

Slackness can resemble in this manner:

If a soldier marching in an orderly fashion, in a crowded lineup, becomes slack and falls, he will get crushed under the feet of others, and he will drop behind so much that it will become challenging for him to catch up to his fellow soldiers.

Imagine some cars are traveling bumper to bumper on a busy highway. If one driver loses focus, his car will fall behind. He will suddenly come to his senses and realize that the others have passed him, and then it will be tough for him to compensate for his lapse. However, if he accelerates, he may face inconvenience or even crash. So, he should not lose his self-restraint.