No writer wants her or his message derailed by a poorly chosen word that can trip up the reader. Many English words look and sound similar, but they have very different meanings. Choose the correct word for the context, and your content will shine. And you will look smart. Here is a link to a great blog post outlining some of these pairs, referring to Inigo Montoya of Princess Bride fame:

The Inigo Montoya Guide to 27 Commonly Misused Words | Copyblogger.