kǔ kǒu pó xīn
earnest and well-meaning advice (idiom); to persuade patiently
kǔ kǒu
lit. bitter taste (cf good medicine tastes bitter 良藥苦口|良药苦口)
fig. earnestly (of warning, advice)
liáng yào kǔ kǒu
good medicine tastes bitter (idiom); fig. frank criticism is hard to swallow