苦あれば楽あり [くあればらくあり] is a favorite saying of mine. But in looking around the internet, I think that some of the translations into English that I see (e.g. “every cloud has a silver lining” or “no pain, no gain”) don’t quite cut it. Granted, they may be the closest native English proverbs we have available, but my goal isn’t to get you to understand Japanese in terms of English equivalency, but rather in terms of understanding Japanese as Japanese.
苦 has a variety of meanings, but all tend to fall into the area of bitterness/hardship/suffering. あれば simply means “if exists” or “if (one) has.” 楽 is often used when describing music (e.g. 音楽) but also has connotations of fun, ease, or comfort. All this taken together, the phrase really means something more like “if you struggle through bitter hardship, you will have ease.”
There’s a flavor (pardon the pun) to this that, in my opinion, isn’t quite there in either of the aforementioned English versions. “Every cloud has a silver lining” seems to be too fairytale-ish and passive for me, and “no pain, no gain” doesn’t really talk about what the “pain” is. I mean, you can hit yourself in the face with an ice pick repeatedly and cause pain, while experiencing no demonstrable “gain.”
A related phrase is 苦は楽の種 [くはらくのたね] or “bitterness is the seed of ease.”