In fact, when in doubt, just go with the most masochistic option available.
(Ryouyaku wa kuchi ni nigashi; “Good medicine is bitter in the mouth”)
Good advice is hard to listen to. The advice that we most desperately need is that which points out and helps us to escape our most damaging failings… which is exactly what we least want to face and grapple with. Unlike the English equivalent line about “a spoonful of sugar,” this saying primarily refers to the pain of receiving this kind of feedback.
We begin with the noun 良薬 (ryouyaku), literally “good medicine.” This is marked by the particle は (wa) as the topic of discussion in the sentence. Next we get the noun 口 (kuchi), “mouth,” marked by the location particle に (ni). What is it in the mouth? The adjective 苦し (nigashi), “bitter.”
This saying appears in the Edo iroha karuta set, but not under り as you would expect from modern orthography. Instead, this is the れ entry. According to older conventions the compound that is now りょう would have been written as れう. (The most amusing example of this phenomenon may be けふ – which, read in modern terms, would say kefu – as kyou.
This saying is derived from the first part of the same longer Chinese passage that gave us 忠言耳に逆らう.
(“Kozou yo, ryouyaku wa kuchi ni nigashi to iu no wa yoku wakatteru no da ga, kore kara no chuukoku wo sunao ni kike.”)
[“Okay, brat, I know all about how good medicine is bitter, but be good and listen to the advice I’m about to give you.”]