Sometimes you calculate absolutely nonsense

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Here is a puzzle from Emms book where i tried hard to solve and finally haven't solved it:
White mates in three.
 
 
Sometimes it happens to me that i calculate with impossible moves (here it was 2... Ke8) or with pieces on their original place when they have moved somewhere else or are not on board any more. I have to keep an eye on that.
 
Any idea how to fix that?