One great HU trainer said the following: "When I feel I played a hand very badly, I will mark that. For example, when I couldn't fold a hand that I should have. I put the marked hands in one file and I have a look at them every week. I summarise how much I have lost in these hands and knowing how much these cost helps me develop a feeling of shame that helps me stay alert next time."
Romsy said the following on the issue:
"There are a lot of mistakes that I write up with my nice pen. How much I have lost on bad river and all-in calls, and at the end of the challenge I am astonished how much I could have won if I always played my A-game."
A good player in a borderline situation always looks for the reasons why NOT to call (or why to start a bluffing campaign), why the weak player focuses on the reasons to call. Many winning higher limit players confess that they lose most of their money in these borderline hands, where they fold not often enough.
The average regular often makes the mistake even at medium limits that they don't fold certain hands easily (like a three of a kind for an overbet, or an overpair for a simple raised pot). Don't fall for this! When you are making the guesswork, it is true that most of the time you will make the worse decision.
According to this, when you are hesitating between a fold and a call in a borderline situation, it is true that you will come out better if you always fold. This is especially true on the turn, as it often happens that your opponent is bluffing and your medium-strong (second/third pair, A-high) hand is the best out there. On the one hand, your opponent's hand has some equity in these cases, and on the other hand, your opponent will still bluff the river even if he didn't get better. And two streets will surely not be profitable if you keep doing the guesswork.
Example no. 1: NL30 SH 88 full 180BB deep gets an overbet push on the river
In this hand, a weaker regular will not let go of a very strong hand, even if he will almost always lose against an opponent playing 19/14 and will receive tragically bad bank odds for his call.
Stacks:
BTN Hero ($55.55)
SB sv107 ($32.23)
BB scabee79 ($53.68)
Pre-Flop: ($0.45, 3 players) Hero is BTN
Hero raises to $0.90, sv107 calls $0.75, scabee79 calls $0.60
Flop:
($2.70, 3 players)
sv107 checks, scabee79 checks, Hero checks
Turn:
($2.70, 3 players)
sv107 checks, scabee79 checks, Hero bets $2.70, sv107 folds, scabee79 calls $2.70
River:
($8.10, 2 players)
scabee79 goes all-in $50.08, Hero WTF ???
BTN Hero ($55.55)
SB sv107 ($32.23)
BB scabee79 ($53.68)
Pre-Flop: ($0.45, 3 players) Hero is BTN
Hero raises to $0.90, sv107 calls $0.75, scabee79 calls $0.60
Flop:
($2.70, 3 players)sv107 checks, scabee79 checks, Hero checks
Turn:
($2.70, 3 players)sv107 checks, scabee79 checks, Hero bets $2.70, sv107 folds, scabee79 calls $2.70
River:
($8.10, 2 players)scabee79 goes all-in $50.08, Hero WTF ???
Example no. 2: NL100 - three of a kind, river question
Let's acknowledge that all the higher limit regulars would prefer a fold.
Stacks:
UTG Sarah Ton1n ($100)
CO work2do ($100)
BTN Hero ($138.40)
SB AndTheWalrus ($107.05)
BB bertjan123 ($69.65)
Pre-Flop: ($1.50, 5 players) Hero is BTN
Sarah Ton1n raises to $3, 1 fold, Hero calls $3, 1 fold, bertjan123 calls $2
Flop: 
($9.50, 3 players)
bertjan123 checks, Sarah Ton1n checks, Hero bets $6.50, bertjan123 folds, Sarah Ton1n calls $6.50
Turn:
($22.50, 2 players)
Sarah Ton1n bets $13, Hero calls $13
River:
($48.50, 2 players)
Sarah Ton1n bets $77.50, $77.5 to Hero ($115.9)?
UTG Sarah Ton1n ($100)
CO work2do ($100)
BTN Hero ($138.40)
SB AndTheWalrus ($107.05)
BB bertjan123 ($69.65)
Pre-Flop: ($1.50, 5 players) Hero is BTN
Sarah Ton1n raises to $3, 1 fold, Hero calls $3, 1 fold, bertjan123 calls $2
Flop:
($9.50, 3 players)bertjan123 checks, Sarah Ton1n checks, Hero bets $6.50, bertjan123 folds, Sarah Ton1n calls $6.50
Turn:
($22.50, 2 players)Sarah Ton1n bets $13, Hero calls $13
River:
($48.50, 2 players)Sarah Ton1n bets $77.50, $77.5 to Hero ($115.9)?
Example no. 3: NL100 HU - KK
Of course, we don't think this hand should have been folded, but it is a good example of our very strong hand not being enough in a borderline situation. (In heads-up, KK equals the nuts even 383BB deep).
Pre-Flop ($1.50, 2 players) Hero is SB
Hero raises to $3, staceyanne79 raises to $14, Hero raises to $35, staceyanne79 raises to $79, Hero calls $44
Flop ($158, 2 players)
staceyanne79 bets $97, Hero calls $97
Turn ($352, 2 players)
staceyanne79 goes all-in $207.55, Hero calls $207.55
River ($767.10, 2 players, 1 all-in)
Final Pot: $767.10
staceyanne79 shows a pair of Aces
Hero shows a pair of Kings
Always be relaxed when playing
When you are tired when playing, you lose attention. Going through your hands the next day, you will often notice that you could have done much better, and taking all pieces of information into consideration is very-very important and can spare you a lot of money.
Sometimes being well-rested is not enough to make the right decision. For example, you might think that you have squeezed, which makes your opponent think you have a weaker hand, while in reality you made a simple 3bet to the UTG. Or you forget to cbet on one table because there was action at an other one, and when you glance at your table, all you see is you have a marginal hand compared to the board texture and play check/call or check/fold. However, you could easily have made a cbet, being the preflop aggressor.
The more tired you are, the more often these mistakes occur. It is definitely not worth playing when you are tired, as it will only make you lose and not even understand why. And the next day you will be banging your head to the wall when analysing your hands.
That is It
With this, we have gotten to the end of our ebook.
Wow, that's a lot of stuff! Do I have to learn all that to be a winning player? you could ask.
Well, obviously we have put together here gameplay tips that we ourselves found profitable. We need to confess, however, that we ourselves do not always succeed in following these guidelines. Believe it or not, we face the exact same problems day to day, but there is no other option. If you want to get to NL100 or higher some day, you need to go through all this and more.
