더라면

If only it had happened

It reaches back to something that did not happen and imagines it did: if only I had known back then, if only the teacher had been a little kinder, if only you had not done that freestyle. Regret is built in, and the sentence usually continues with how things would have turned out differently. Compare plain 았으면, which can also be a wish about the future; this one is firmly about the past.

Register: neutral, usually wistful or rueful