I often see and hear mistakes with these two words.

Problem:
These words are spelled similarly but have different meanings.

Explanation:
The word “affect” is spelled A-F-F-E-C-T.

• As a verb, the word “affect” means to act on or to produce a change in, as in “You can affect her attitude toward education.”
• As a noun, the word “affect” means emotion or feeling, as in “The psychiatrist said that the patient’s affect could be a symptom of schizophrenia.”

The word “effect” is spelled E-F-F-E-C-T.

• As a verb, the word “effect” means to bring about or make happen, as in “Many people believe that he cannot effect the change that he is promoting.”
• As a noun, the word “effect” means consequence or result, as in “The effects of Hurricane Ike could be seen throughout Houston and Galveston.”

It is a common English blunder — at least in American English — to use one of these verbs as a substitute for the other one. It is also a common English blunder to use one of these nouns as a substitute for the other one.

I believe that mistaken interchanging of these two words is due to mispronunciations, which drive misspellings.

Solution:
Memorize the verb and noun definitions of these two words.