Dear Student
There are many diseases that cannot be cured. No medicines are there yet to treat them like AIDS or cancer. So it is better not to get the disease rather than to cure it. If we can prevent the disease to occur then no medicines are required. More over the medicines have several side effects that may destroy some other system while curing a disease. Thus it is better to prevent the disease to occur than to cure it by applying medicines. Hence prevention is better than cure.
Regards