There different factors that can trigger or behaviour one is your thoughts, Biological or environmental. We cannot do much about environment but if properly worked on thoughts and little bit of biology things can be different. A proper assessment is required if the depression is due to biological reasons only therapy or thinking helpful won't help. Sometimes medical intervention might be needed. Also thought about feeling low need proper therapy and not just think positive let's do things that make me happy type of approach. A 10 session thought Managment therapy is required.