Watch your tactics

Before you execute a tactic, you should check it. If it goes against you, you probably shouldn't use it. Here's an example. This puzzle is from the "The Usborne Internet-Linked Complete Book of Chess."

After solving this puzzle, check out the next position. It is very similar with a few  differences.

(This should not be a puzzle. Just click solution.) As you can see, you should check your tactics!

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