Anything that influences how you feel and how manageable your life feels can be an influence. Both positive and negative, they can be in many forms, such as a person, a behavior, or a thought.
It’s easier said than done to weed out negative influences, especially because sometimes the same thing can cause both positive and negative effects. Maybe someone provides you with companionship, but says things to make you feel guilty, or things you tell yourself help you feel in control, but you obsess over them. How can you differentiate when negatives are outweighing benefits?