“Just do tactics.”
I think we’ve all heard this before.
And honestly for a lot of players, it is decent advice.
But here’s the problem.
When you sit down to solve a tactics or calculation problem, 99.99021% of the time there is going to be a solution, and you know that.
In a real game, there’s no guarantee your calculations will result in finding a ‘solution’ in any given position.
And contrary to popular belief, there’s also no one sitting next to you during a game screaming “omg bro, if you sack your queen you have forced mate in 26!!!”
What many players eventually become awakened to, is that there is a disconnect between the ‘practical’ calculation they do during their actual games, and the ‘puzzle’ calculation they do at home.
Before going further, though, I want to actually say that these ‘flaws’ do not mean conventional tactics or calculation puzzles are a waste of time.
Occasionally I hear players complaining ‘I would never get a position like this in a real game’, often as an excuse for failing to solve a position.
But I would argue that the whole point of training in the first place is to push yourself to levels beyond your current ‘baseline’.
This is going to involve solving at least some moderately difficult positions, for your respective level.
If you can sustain this, then the things that previously felt difficult to calculate in games will gradually feel easier.
Practical Calculation
As opposed to what I’d call ‘puzzle calculation’, we have ‘practical calculation’.
Puzzle calculation is the celebrity who everyone knows and admires, and receives all of the media attention.
Practical calculation is the behind-the-scenes guy doing all the grunt work, making sure everything runs smoothly, but never gets seen or acknowledged by the public.
It’s one of the reasons you can look at the games of great positional players like Karpov and have the impression of it being ‘effortless’, yet producing such a game yourself is a completely different story.
What often gets overlooked in many of the games of players like Karpov, are all the small calculations they had to make at various points, to ultimately culminate in such ‘masterpieces’.
One thing I’ve found among new students is that they often struggle when I give them positions that involve doing more of this ‘practical calculation’.
This is often because they’ve become so accustomed to the idea that if a position is given as a ‘puzzle’, there must be a forced win, or something of that character—which I generally see as a shortcoming in a player’s ability to look at a chess position in an objective manner.
Many of the ‘solutions’ to such exercises I give students often require:
finding the best way to minimize a disadvantage
justifying a positionally desirable move through calculation, which otherwise looked impossible to play
or steering clear of a line which looks natural, but if paying attention to the opponent’s ideas carefully actually will backfire

Unfortunately, what I’d consider as ‘practical calculation’ is still for the most part neglected in chess media/literature, despite its relative importance for players looking to improve their game.
I don’t really see this changing any time soon, largely because of how “unsexy” the topic is, but I have some plans in the works.
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Cheng's Practical Chess Exercises is one of the few books that offers some relevant training here
A Question of Modern Theory by Lipnitsky states either a position is critical or settled. Puzzle calculation assumes everything is critical. Most amateurs, including me, sometimes don't understand a position is critical (from probably bad thinking habits) and then don't even check for answers properly to begin with. I think the most shining examples of this is missing short calculation solutions (mates in 1 or 2 or maybe pawn moves of some some sort)... Can Kabadayi has a course on that, and Polgar's 5334 book is for it. There's also pattern books for positional solutions. So I'm not quite sure if calling it practical calculation is correct, because they're still puzzle solutions (just ones that we don't train with online tactics trainers unless you are aware of this deficiency).