"EFFECT" and "AFFECT"

"Effect" is a noun meaning result. "Affect" is a verb meaning to influence. Ex.: The new policy had a significant effect. The weather can affect our mood.

"PRINCIPAL" and "PRINCIPLE"

"Principal" refers to a person in a position of authority or the primary part of something. "Principle" means a fundamental rule or belief. Ex.: The school principal addressed the students. The principal reason for our success is teamwork. Honesty is an important principle to uphold.