A lemon is a citrus fruit known for it's bright yellow color and distinctive sour taste. Every human reacts to each intake of food, that's where the taste bud come in. Once the taste buds detect what's coming in, they send a signal to the brain, and the expression shows on the face. When one takes honey or any sugary food, the person usually presents a bright or happy expression. When someone tastes something weird, bitter, or sour, the expression is different.
A lemon is very sour. When someone sucks on a lemon, the expression on their face is often unpleasant. This means that an expression resulting from an unpleasant situation or circumstance could indicate disappointment or frustration. It could also mean that the person is going through a difficult time, and everything at the moment seems off.
Everyone experiences such moments at some point in life. The world is not perfect, and these moments are not forever, they are temporary.
Image by Shane