Close in meaning and spelling, affect and effect might be the most commonly confused in all of English! Let’s look at the difference:

To AFFECT (verb) means to influence or to cause a change:

1. Norman’s injury didn’t affect his desire to compete.
2. I don’t feel so good. Something is affecting my stomach
3. The families were deeply affected when they visited the memorial.

An EFFECT (noun) is the change that results.

1. The injury had no effect on Norman’s performance.
2. The medicine I’m taking is working to good effect.
3. Leaving the memorial had a restorative effect on the family.