Before going beyond ranges, let me first give a quick review of what range theory is.
According to range theory, a player in a given position will have a given range. A range refers to the possible combinations of two hole cards they can have. A card combination is either in the range, i.e. consistent with past action, or it is not. When faced with a decision, some (or possibly none) of the combinations will fold, some will check/call some will bet/raise, and some will shove. All the combinations that bet/raise will do so with the exact same amount to obscure intentions.
This is the standard theory that almost all poker players follow.
However there has been no hard proof that this is the best way to play the game. In fact recent findings from AI research seems to indicate that it is not the best way to play.
What we can say in it’s defense is that playing based on ranges is a really solid and strong way to play. And it has the advantage that it is easier to learn and reason about.
So if range theory is wrong, what is right? The correct way to play seems to be more deceptive in a way. Instead of always playing the same situation the same way, you should play it differently different times, so the theory goes. As an example a given hand preflop may bet for value most of the time, but then occasionally limp to sneak up on the unwary.
Further, because of the increased deception that comes from playing differently different times another possibility is enabled. Betting different amounts with different holdings. Betting big with big hands and small with small hands is normally a surefire way to tip the other players off to what you are up to. But if you bet big 60% of the time and small 40% of the time it’s not as predictable anymore.
Another consequence of using some randomness in how you play is that a given play is not “correct” or “incorrect” by itself. Well it can be incorrect if it’s really stupid. But more often a given play will rather be on the scale “do this rarely” vs “do this a lot”. This is of course very dangerous for human psychology, as any play can be rationalized, and rationalization is a big bankroll killer.