Just like a person is diseased. He is advised by the doctor that "You shall not take such and such things." So he is starving or he is fasting. Suppose in the typhoid fever the doctor has advised him not to take any solid food. So under the instruction of the doctor, he is not taking any solid food. But suppose his brother is eating some bread. Oh, he likes that "If I could eat." That means within himself he has got the tendency for eating. But out of fear that "If I eat, there will be very bad reaction of taking solid food," therefore, by force, he is not eating. Similarly, there are so many things which you are refrained from doing by force. That sort of abstinence will not make you progressive in spiritual life, because you have got little independence. So anything cannot be done by forcing you.
You cannot force even a child. He'll revolt. By force, you cannot train a person that "You must be refraining from all these things. One may be refraining from enjoying materially by somehow or other, by force but one who is spiritually advanced, he is not forced. He is voluntarily giving up. That is the difference. How voluntarily giving up? That is by vishaya vinivartante, the higher taste. He has found something sublime, so sublime that he doesn't care for material enjoyment. If you simply try to make it zero, that is not possible. If you get better engagement, to try to engage yourself always in the better engagement, then these material activities will be zero. That is the criterion of spiritual life. When we get a taste of spiritual pleasure—pleasure in Krishna consciousness—we can give up all material pleasure.
Ref: Bhagavad-gita 4.10 Lecture on March 30, 1974, Bombay, by Srila Prabhupada (Founder – Acharya, ISKCON)