Simplest way to know that Kf3 is losing in this position?

Hi there, I am new to (serious) chess and learning endgames.

I found this position in chess.com endgames, with white to play, and Kf3 is losing (well, drawn, but in a winnable position). I can see this by explicitly calculating...

1. Kf3 Ke7

2. Kf4 Kf6

at which point it is clear to me that the position is drawn. But in an endgame, such a calculation takes me precious seconds. Is there any general principle by which one more easily knows where to move here, or would an expert decide this position by explicit calculation as well?

I see - thank yo for the help. So from what you wrote it seems that if you had this position in a game, you would explicitly check those lines, realize that only the rightmost one is winning, and then decide on the move. If I understood you correctly, there is no single "endgame principle" which makes it clear without calculating a few moves which line is winning for white?

For this example its all about knowing the key squares.  Once you gain some understanding of that, youll know what to do.

Start with the basics.  Understand that the key squares are f6-g6-h6.  Which king can get to a key square first?  The black king is 2 square from the key square f6, while the white king is 4 squares away from f6.  So that will tell you that 1.Kf3 wont work.  So now we move on to the key square g6.  The black king can get to g6 in 3 moves, while the white king will take 4 moves.  So you know that wont work.  Now we get to the key square h6.  It will take both kings 4 moves to get to h6, but white moves first. 

That's brilliant! Great, that really makes it simple, thank you!

Keep it simple.  Always remember that the key squares are the 3 squares directly in front of and 2 ranks ahead of the pawn.   The point is to control them squares.  Which is why rook pawns have rules of their own.

Actually 2 ranks ahead of the pawn.

Thank you and corrected.  I guess i should start paying more attention to what im posting.

Actually always two ranks ahead of the pawn but either  one or two ranks ahead of the pawn after the pawn has crossed the crease, or two or three ranks ahead if it's on its starting square. Except when it doesn't work, which is quite a lot especially with rook's pawns. E.g. White to play here can reach a key square, but it doesn't do him much good.

The "two rank" rule applies always, excluding the case where the pawn is under direct attack by the opponent king.

In your example, the king cannot reach at a square two ranks ahead of the pawn, right?

The rooks pawns are always an exheption.

The king can reach e.g. e5, but the  pawn will then be under direct attack as you put it. Nobody mentioned the direct attack bit before.

The two rank rule doesn't apply to pawns on the seventh rank, but the one rank rule still applies. When the one rank rule applies direct attack by the enemy king isn't relevant. E.g.

The exceptions are not altogether restricted to the rook's pawns. White to play here can reach either of the key squares f7 or f8 but it still doesn't do him much good.

Actually the two rank rule is already an overkill when the king has reached the 6th/3rd rank. One rank is enough.

@pfren

By "passed the crease" I meant on the 5th rank or above (for the pawn that is).

It isn't a race to occupy the key squares. It is usually in the attacker's interest to occupy a key square with his king, but the defender is then interested only in preventing the  attacker's king from doing so. In this case should  White start Kf3, Black can exclude the White king from the key squares by occupying one as you show, but this is just as good.

In general the defending king wants to occupy the critical squares of the pawn (those from which it can capture the pawn) and the attacker needs to take account of that. In this example White should initially ignore the key squares and concentrate on preserving his pawn.

Even if the pawn needs some support from the king, playing by key squares is not always necessary or most efficient. In this Black to play position the pawn needs some action by the king but the key squares are most efficiently ignored by White.

Of course, with White to play from the same board layout key squares are quite irrelevant.

If your goal is to draw a won endgame then yes, 1.Kf3 works.

I'm not disputing that 1.Kf3 draws, merely pointing out that occupying a key square is a goal for White, not Black.

In the first variation of the second example I gave, Black does indeed occupy a key square before White can, but it doesn't draw.

An experienced player usually looks for a win condition (if they need to find a winning idea) or a draw/loss condition (if they already know they're winning and need to avoid screwing up).

In this case a studied player knows what a few of the draw conditions looks like e.g.:
(white to move in the 3 diagrams below)

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An experienced player is also familiar with the idea that several king paths are equivalent. For example let's ignore the black king for a moment and pretend the white king wants to go to g5. Well 1.Ke3, 1.Kf3, and 1.Kg3 are all equally as fast.

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And finally, an experienced player has seen these sort of endgame practice positions before.

So having the draw conditions in mind will make 1.f3 look unpleasant, knowing the equivalent path thing will make 1.g3 look almost automatic, and having seen these sorts of ideas before will make the winning idea almost automatic. At the end of a long game, a strong player is still likely to calculate a bit, just to check things (out of habit more than anything) but, yeah, this is my attempt at answering your question.

When you learn what youre talking about let me know.

Re post #17 by @llama47.

But be aware that the last one doesn't draw whichever side has the move if the pawn is past the crease, i.e. with the pieces moved up a rank.

You'd take any notice?

I'm just paraphrasing Averbakh.

Black can reach a key square in the second diagram I posted above, but can't draw, while Black can't reach a key square in the diagram below but can draw. Carry on thinking Black's aim is to get his king to a key square if it makes you feel happy.