I will avoid the easy double-entendre opportunities afforded by pliant, willing “so“. Of grammar’s eight Parts Of Speech, “so” generously serves a full five of them with an ample dozen shades of meaning. She began her magnanimous life, however, in very opposite circumstances – a tightly limited existence as a reflexive pronoun stem (say what?) for language’s vastly ancient Proto Indo European (PIE). She was just a little servant stem-word that called out to emphasize those moments when the pronoun-boss was reflecting back to his own self. Like: He was talking to…whom?… to himself. In this modest way she toiled for a few thousand years, up through Greek and Latin, then into Germanic and Norse and Old English. Ever so(!) slowly she worked her way free of the stem straightjacket. Adding “as” and “in that way” to her repertoire she started to stand alone as sweet supplier of emphatic services, and English turned out to be wonderfully appreciative. English gave her free reign, and in a short few hundred years she filled her dance card with new partners. There’s no way to know how the tipping point was achieved, but by 1530 so-so had come to mean something “mediocre”, and by 1596 so-and-so meant “something of unspecified value”, making the dance floor look pretty wide open. In what way, when, why, farewell, sarcasm, curiosity, agreement, affirmation, approximation, thereupon, likewise, disinterest, orderliness, and many more now compete for her hand. So! Things no longer had to be just so. English was liberal, so much so that PIE certainly wouldn’t recognize it’s own anymore. And, so what! Times change, and so be it. So became an enthusiast of the vernacular, and has remained so. She seized her opportunities, so got the prize of ubiquity. We find her everywhere, and enjoy her so! And so on and so forth. So there!
Etymological illuminations brought to you by Jane