Why most have bad habbits than good?

well if we have to be good then we need to ahve both phusical and mental discipline. we cant do wat we like when we like. but otherwise say if r bad we do wat we like when we like. this life is so designed that thinghs we liek the most will casuse us harm and things we dont really like much will bring us good things. for example we love ice creams ..but we cant eat it too much cuz it will create health probs. we hate medicines, we hate to sit and stuy for our exams but it will give us good benefits.