柠檬不比心酸西瓜不比心甜
[níng méng bù bĭ xīn suān xī guā bù bĭ xīn tián]
The bitterness of lemons cannot be compared to heartache, just as the sweetness of watermelons cannot compare to true sweetness felt from one's heart. This reflects the idea that only true emotions, such as heartache and happiness, are real and deep experiences.