たらいい / といい

といい and たらいい say what you hope for: "I hope…", "it would be nice if…". といい follows the dictionary form or the ない-form, たらいい the たら form, and both usually end in な, ね or のに.

Hoping for someone else

To wish the listener well, といいですね is the set phrase.

With んですが or けど at the end, the hope comes with doubt.

"If only"

With のに, the wish runs against the facts: it isn't so, and you wish it were.

Giving advice

たらいい and といい can also tell someone what to do: "you could…", "the thing to do is…". This is gentler than ほうがいい.

With a question word, たらいい asks for advice instead: どうしたらいいですか, "what should I do?". ばいい works the same way in all these uses.