Affect and effect are sometimes used incorrectly. Here is what Merriam-Webster says:
the conscious subjective aspect of an emotion considered apart from bodily changes; also : a set of observable manifestations of a subjectively experienced emotion
1. to make a display of liking or using
2. to put on a pretense of
3. to tend toward
4. to produce an effect upon
1. something that inevitably follows an antecedent
2. an outward sign
3. power to bring about a result
4. movable property (plural : effects)
5. a distinctive impression or the creation of a desired impression
6. the quality or state of being operative
to cause to come into being
That’s a whole lot of definitions. I’m going to pretty much ignore most of them and focus on the most commonly used (and confused) meanings. Basically, affect has to do with pretence; or the creation of an influence or effect. On the other hand, effect has to do with accomplishing something; or the result of something.
Affect – Doing something with pretence (e.g. I affected a happy mood despite being depressed); Bringing about an effect (e.g. My depression affected the moods of everyone else).
Effect – Achieving a final result (e.g. The board effected a change in the company); The result of a phenomenon (e.g. The change had a negative effect on the company’s profits).