C.s. Lewis said this quote

The pretence leads up to the real thing. When you are not feeling particularly friendly but know you ought to be, the best thing you can do, very often, is put on a friendly manner and behave as if you were a nicer person than you actually are. And in a few minutes, as we have all noticed, you will be really feeling friendlier than you were. Very often the only way to get a quality in reality is to start behaving as if you had it already.