Why People in Spiritual Life Fall?

Question: How is it that there are many people whom I know have fallen quite badly after laboriously ascending the precipitous steps in spiritual life?

"...Many spiritual aspirants climb up to a certain height on the ladder of Yoga and are then IRRESISTIBLY swept away by the TEMPTATIONS.... They lose their POWER of discrimination and RIGHT understanding.... The man who is endowed with STRONG discrimination, SUSTAINED dispassion, KEEN self-analytical power, and BURNING desire for liberation can resist temptations. He ALONE can be really happy. He alone can attain the highest goal of life --- the final beatitude or sublime vision of the Infinite." (Swami Sivananda's commentary on Gita 9:20).