Be careful to not make this mistake! It's not a huge deal, but most of the grammar things I've brought up aren't. Learning how to use these words will make editing with a professional editor so much easier in the long run.
Correct: reason is that
Incorrect: reason is because
The reason she hates him is that he's annoying.
The reason for bad business today is that the weather was really ugly.
The reason she said yes is that he asked so nicely.
his reason for eating the pie is that she told him not to.
Authors/writers: Make sure you're on my list of authors!