I subscribe to Chess Today which gives much interesting material. There are often fragments of endgames and typical blunders as well as annotated games and ideas and chess news. There is also a daily test position (sometimes more than 1) which are fun to solve. Very often, the answer to the puzzle is just a single move which will be the key to the solution. However, it is still good to calculate deeply, and even play the puzzles out, as you can unearth some variations.
For instance, today the puzzle was from the game Malakhatko-Wieczorek Krakow 1999 and the following position was given:
It is white to play, and it didn't take me long to find the key 1.Ng4+! which weaves a mating net around the black king. 1..fxg4 [Forced as 1..Kh5 loses immediately to 2.Rxh7#] 2.hxg4 [With the threat of Rh1 mate] 2..g5
In this position, the first thing that comes to mind is 3.f5 with the unstoppable threat of 4.Rh1#. But a slightly deeper look shows that mate can be stopped. After 3.f5 black has to play 3..Bf1 sacrificing the piece back again 4.Rxf1
Now the only way to stop mate is to sacrifice a rook by 4..Rc2+ 5.Kxc2 when black must keep with the checks 5..Rc8+
Around here you should have noticed that black's king and pawns cannot move. This allows the great swindling chance of sacrificing black's final rook. In fact, white's only winning chance here is to play 6.Rc7 giving a rook back again and heading to a winning rook endgame. Any king move will lead to black playing with a kamikaze rook placing itself next to the white king continuously. If you haven;t seen this theme before, try playing it out. The white king can't escape!
Of course, if we go back to position before 3.f5 was played, we can look for other options:
Forcing lines are the best to try out first. So 3.Rh1+ and then it is not hard to see that after 3..Kg6 4.f5+ Kf6 5.Rh6 is mate.
So I guess what I'm saying is that seeing a key move and then having that single move as the answer isn't the whole story and it is good for your chess to look for all possibilities in positions, and even to play them out to see if there were any possibilities that were missed.