If you want good health, you must insure that your diet is well-balanced and complete. You wouldn’t just gobble up anything edible that comes your way. Spiritual food should be approached with equal care. The practices you choose should be genuine and complete. Sakyapandita said that when we’re buying a jewel or a horse—and the same would apply these days to buying a car or a house—we shop around and ask others for advice, but a wise or unwise purchase can only affect our fortunes in this life. The spiritual practices we undertake can assure or jeopardize our well-being throughout many future lifetimes, and so it is essential to make a wise choice. Milarepa said that unless the teachings we practice are free from errors and have come down to us through a living and uninterrupted tradition, time spent meditating in a mountain retreat will just be self-inflicted misery.
From The Three Principal Aspects of the Path by Geshe Sonam Rinchen, page 40