Ok, I'm playing poker online and I'm faced with this situation:

My cards: K A
Remaining effective stacks $9
Board: 4 7 K 5 6
Pot: $2
Hero bets $1.5, Villain raises to $4.5

What do I do?

This is an extreme example, but milder examples of this happen to me way too often. I play on autopilot on multiple tables and suddenly I'm faced with a decision and I'm not sure exactly how I ended up there.

It's easy when given a hand history to analyse to rationalise your decisions on every street, but the bottom line here is that too often I sit at a poker table and need to make a decision and cannot even remember exactly how the hand I'm in played out. If you think that this is preposterous I have this challenge to you - next time you have a river decision to make, take five seconds out to spell out in your mind the following:

Who bet/raised/called on every street up to this point? Remember to include the ones that subsequently folded, do you still remember who they were and what their positions of the table might do to modify the ranges of the people still in the hand? Do you have an idea what their hand ranges were on every street? Were there any timing tells? Exactly what amount was bet into what pot size on every street?

If you're honest with yourself I am convinced that the vast majority of beginners are no better than me and will have trouble recollecting at least a couple of details. I found that if I play two tables I cannot keep track of everything on both tables (including hands I'm not in)

We talk a lot about forming hand ranges for people, but the very idea of forming a hand range relies heavily on us paying attention to and remembering what the actions in a hand were.

I won't be so crass as to assert that memory or recall is the most important poker skill. What I'll say that it is arguably the most overlooked of the important poker skills in beginners especially.

As with so many things in poker this applies 'on every level'. Poker databases gives us a proxy to long term memory, in that it gives us statistics to go by where memory fails. If we have a guy on a high agression factor and all his stats indicate that he raises way way too often, he raises us we think he's full of shit and we shove - statistics fall short when he min-raises with rubbish and gets folds from terribad players all the time, making his bad play super profitable for him - but he basically never raises a proper bet size and he did this time. Statistics told us - frequent better, he's full of shit. Memory tells us - he always min-bets trash - he never bets a decent amount. He must have the absolute nuts.

It's probably worth working on the old memory.