SpongeBob has a difficult time sleeping at night, worrying too much about the Krusty Krab facing bankruptcy issues due to him adding too much mustard to a Krabby Patty.
Towards the end of the episode, SpongeBob arrives at work, feeling very tired, and goes to sleep in a barrel of mustard. As he is taken out of it by Mr. Krabs, he confesses that he could not sleep the preceding night due to his insomnia and then proceeds to cry tears of mustard. This gives Mr. Krabs an idea to have SpongeBob cry said tears of mustard onto the Krabby Patties as a means to make more money.
SpongeBob, Squidward, and Patrick have to search for Mustard after SpongeBob uses it all up. It is also learned that in the series, mustard, ketchup, hot sauce, and mayo can all be mined like gem stones.