This is part of the difference between series.
Another common pair of words I see mixed up is “then” and “than”. Luckily, telling the difference is easy.
“Then” is always used in reference to a sequence of events, as in:
We went to the store, then we came home
“Than”, on the other hand, is used to compare things, as in:
My dad is stronger than your dad.
A trick to remembering them is “then” has an “e”, and “event” starts with an “e”.