Beshalach: Sweet Waters of Being Happy, Joyous, and Free
The Torah relates that the Israelites came to Marah, "...but they could not drink the waters of Marah because they were bitter" (Exodus 15:23,25).
We understand the verse to mean that the water was bitter. The Baal Shem Tov said that "they" refers to the Israelites, not the water. Because the Israelites were depressed, angry and bitter, the water tasted bitter to them.
It is a common phenomenon, that if a person is deeply depressed, his food may taste bitter to him. The Israelites were grumbling about leaving Egypt, and were dissatisfied with the water available to them.
We tend to feel dissatisfied with things, and we attribute our dissatisfaction to the things we have as being defective. The Baal Shem Tov is telling us, "If you feel dissatisfied with anything: your job, your car, even your spouse, don't blame them. You are probably unhappy with yourself, and you are projecting your dissatisfaction onto them."