柠檬再酸不及心酸
[níng méng zài suān bù jí xīn suān]
This phrase translates to 'Even if lemon tastes sour, it cannot compare to the bitterness in my heart.' Using lemons to symbolize sourness emphasizes that no matter how sour a lemon might taste, emotional pain surpasses such physical sensation. Lemon, here, stands as an analogy for bitter situations or memories causing emotional distress beyond comparison.