Live - psychology, online - math.
I don't think this is true statement. If you play with talkative player, then maybe it can be more about psychology, but there are players who just turn into a stone while in a hand. You have to have solid strategy for both online and live. A very good advice I heard from one of the poker pros (don't remember who was that, but it was some high stakes poker player on twitch) was to follow the correct strategy and use
tells only in close spots. Also is not poker psychology more about how players play more then live tells? I think it is and it apples to both online and live.
Live poker may had been more about psychology than the strategy 20 years ago, but definitely not now. More and more online players have big successes live. BTW. talking about old poker, it is fun to watch
wsop from 80s and 90s, because you can see how much the game has changed
.