If you do something out of force of habit, you do it without thinking because you have done it so many times before.

I just locked the door through force of habit, not thinking that Julia wouldn't be able to get in.

I called him 'Jimmy' out of force of habit.

There are so many things we do during the course of a day through sheer force of habit.

I bow my head before meals just from force of habit - it doesn't mean anything.

I turned left onto her road out of force of habit.

See also: force noun (INFLUENCE)