EQ is equity, OOP out of position, cbet continuation bet, EP early position, LP late position, UTG under the gun, Btn button... I am sure you know these Pwll but others looking at this might not.
The significant bulk (I would go as high as 70%) of hands people post where they have legitimate questions or difficulties they are playing out of position.
Position is important purely for equity realisation through having more information to go on and more opportunities to correctly attack an opponent’s range.
Equity comes in two forms: the raw "my hand has X% against a range of Y," and bluff equity "my raise/bet here has X% chance of folding hands with better equity than mine" and these two totals provide us with our equity in the hands and affect the lines we can take and therefore how we and how well we make money.
Playing out of position cripples the bluff EQ and we really rely much more on raw EQ. We open AQo Cbet a J63r board and get called… what are we doing on turns? Check folding 80% of the deck? If we have the same board with the same hand but have position on the opponent and they check call a cbet, we now decide most of the time how the turn plays out (on a side note, this is why learning when / how / why to donk bet flops and turns is important as it negates one key benefit of position – if they are checking back turns more than ~70% of the time we should donk). If we get a J63T J63K J63A J63Q we can decide whether to bet or check, and relate what to do to opponent tendencies, our history with them, and board textures. 4s may check call flop then check fold turn. We win due to bluff EQ. If we decide to bet a J63K / J63T flop and turn, it is unlikely because we think we have the best hand; it is more because we turned outs which allows us to continue to pressure our opponents ranges through the combination of raw EQ (a result of our actual hand) + bluff EQ (a result of our perceived range of hands) being high enough to legitimise a bet. On another side note, this is the #1 benefit of suited cards (also connected cards to a degree). We are not playing them to flop / turn / river flushes. We are playing them because on rainbow boards we can turn an additional 20% equity which means a lot of the time with position, raw EQ and bluff EQ we can bet again and take down pots where our raw EQ maybe was as low as 20-25%. This is a huge win. Anytime your opponents fold in spots where they have 40% or more equity this is huge for us, and this happens primarily when having position on the villains (if we bet 75% pot they only need 30% to breakeven on a call: 0.75 / (0.75*2 + 1) = 0.75 / 2.5 = 0.3 where pot is 1 for simplicity).
Ex. we have 88 vs TT on a 3K7A6 run out. 88 can fold out TT on this run out, so raw equity is 2 outs post flop, but against some players bluff equity will be as high as 90%, so betting 88 wins as our bluff equity is so high.
Playing OOP we have less information, and we lose a significant edge is realising our equity. This is not just for instances of getting to showdown, but also knowing when we can bet for value or as a bluff. In the above example (KK on KQJTx), if the positions were reversed, if they check call flop and turn then donk bet river for 70% pot we can decide based on their tendencies if this is only really a straight, whereas if they check we have an easy value bet targeting 2 pair hands and they don't know where they are at as we could just be betting because they checked, so a well targeted value bet gets called. In the situation you were in, we don’t know if they are betting the river because they have it, or if they are betting the river because we checked. This is the perpetual quandary OOP play causes. Again having KK with position, the same is true for them. If they’re sitting there with QJ and they check and we bet, they don’t know are we betting because we have “it” or because they have checked and this is a great card for out bluff EQ.
Take the 88 vs TT and have a AK376r run out. The player who has position has a significant edge in terms of how the hand plays out.
Most people know to open a tighter range from EP than LP, but most don't know that this is predominately because we are more likely to be playing OOP opening UTG than opening the Btn, they just know it because it is an idea that is so prevalent in poker.
Apply the above idea and add in floating. If you can credibly represent hands to your opponents who will hand read and make folds you can make their life hell playing having position on them. Their ranges narrows as they bet, your range remains relatively open if you call.
This also leads into another idea that when we have position on opponents, force them to fire multiple barrels. Do not play fit / fold poker when you have position except in exceptional circumstances. Make them win, don’t just let them take it. Make them give up on cbets, make them start to check value hands to balance when they check the flop as the raiser, and let them know 1 bullet is not enough. This then leads to players being forced to play very straight forward when they are OOP.
There is more I could add here if I thought for longer. Tear this apart anywhere there seems to be a loose thread. I make mistakes, I am wrong about some things, so please don’t take this as gospel. If I come across some hands when I do reviews and I think to I will post them as examples of how much easier it is to play pots having position.