Japanese conversation runs on aizuchi — the small noises a listener makes to show they are still there. Hai, ee, sou desu ka, naruhodo. English speakers listen silently and Japanese speakers read that silence as boredom or disagreement.

This is the cheapest fluency in the language. You do not need to say anything of substance; you need to make the right noise at the right moment, roughly every clause. Learning four of them changes how conversations feel more than another hundred vocabulary words would.