Modal operators are words, which imply either possibility or necessity, which often form our rules in life. It is not unusual to find people predominantly use one or the other which tends to reflect their outlook on life.
Necessity
Modal operators of necessity are words such as 'should', 'must', 'have to', 'won't', 'need to', etc., that indicate lack of choice.
Necessity people usual have set rules about life and tend to obey rules. They are good planners and have a strong sense of duty.
Possibility
Modal operators of possibility are words such as 'may', 'might', 'could', 'can' that indicate there is choice.
Possibility people like to always have a choice. They do not like to restrict their options in life. They are likely to be less reliable and more hedonistic.