Note: This turned into something that had a wider scope than what I originally intended, so I've changed the title to fit. This thread was previously called "Why people suck at putting Villains on ranges on turn/river". The new title is obvious homage to Fnord's LHE post.

Edit: Okay I'm done playing and running errands and so I'm going to elaborate on what I mean here so that the chance that people will understand what I'm getting at will increase.

So what street do the vast majority of micro and low stakes players play the worst? The river. I see the lack of putting Villains on ranges on the river (and then using that information effectively) as the main reason that this is the case. But when we look at why that is, we blow open a lot more than just the river.

What street do the vast majority of micro and low stakes players play the best? Preflop. Why? The principles of playing preflop are easy to learn, and there are tons of articles and resources talking about it, not to mention tons and tons and tons of starting hand charts. With all of this information, you can get away with not putting your opponents on ranges because most micro/low stakes players don't adjust for their opponents much preflop anyway, and if they do it's more memorized type behavior, not the result of actual thought.

For example, a 10/7 with a 20bb stack opens 3x UTG in FR and it's folds to you with 33 on the button. It's a pretty easy fold, but you probably don't come to that conclusion because you've considered the entire situation, it's probably just a reaction because someone told you that you should call raises with 33 to hit sets except when you have bad odds.

On the flop we have a lot of "memorized" lines and behavior, but not quite as much as preflop. As a result of this type of behavior, micro/low stakes players tend to play the flop slightly worse than preflop. Suppose a 10/7 with a 100bb stack opened 4x UTG in FR and it folded to you with AA on the button and you 3-bet to 12x and Villain called. Then the flop came A83 rainbow, Villain bet 2/3 of the pot and you called. You didn't call because you considered his range and decided on the best line of action, you called because you've been taught to call in this spot.

So now by the time we get to the turn, our "memorized" lines and behavior have become less reliable. There are some, sure, but it's harder to classify them into little groups for mass consumption because there are too many "it depends" factors at this point because there's too much going on in the hand. The majority of micro/low stakes players have left the safety-net of their "standard" lines and actions, and now they are forced to think. To put their opponent on a range, they have to remember what happened way back preflop, then what happened on the flop, and now what's happened on the turn, but the truth is this is too much work so they just react to it being their turn with whatever seems right, and a similar process happens on the river.

And this is why people suck at putting Villains on ranges on turn/river, which also happens to be why people suck at playing the turn/river. But here's what you can do to change this:

1. Put your opponent on a range on every street, every time.
2. Think about why you are doing what you are doing on every street, every time. To do this, you have to have done #1 already, because you have to know what you think your opponent's range is.

Holy crap! Now you have opened up a whole new world of poker and can start doing some really crazy stuff like reading blog posts by ISF and understanding them.