A person's usual attitude or mental state is his or her mindset. If you have an environmentalist mindset, you probably bring your own bags to the grocery store.
Some examples of mindsets include an optimist's sunny perspective on life, a business owner's entrepreneurial way of thinking, or an Army general's military focus. Sometimes, a mindset spreads between people in a group and colors the entire group's outlook — psychologists call this groupthink. The noun mindset was first used in the 1930s to mean "habits of mind formed by previous experience."