9- No communication with people
Speaking and communication helps a person to develop their mental faculties and contributes to the intellectual growth of the brain. Being a loner shouldn’t stop you from conversing with friends and family at least.
10- Lack of Stimulated thinking
Exercising your brain is good for you. Remaining indifferent to every situation in life and not thinking nor trying to work out solutions for you is bad for mental development. Ponder over something, think on a topic, stimulate your brain to open up new means of intellectual activity in your brain or else as they say it will rust.
Not utilizing your brain is one of the easiest ways to damage your brain because the more you use it the more it grows.