From any of the first few planes the aspirant, instead of going forward toward the goal, may have such a setback. In exceptional cases an aspirant of the fourth plane may, through abuse of his powers, invite upon himself such a fall that it takes ages for him to return to his earlier point of progress. The aspirant who has such a fall is known as a yoga-bhrashta. Even the yogis are subject to the unyielding law of karma, which knows no exceptions, concessions, or preferences. It is only when the aspirant has the advantage of the guidance by a Perfect Master that the spiritual journey is rendered safe and steady, and it is only then that there is no possibility of a fall or retrogression. The Master steers the aspirant from negative karma in which he might otherwise become involved.
Treading the spiritual path continues for several incarnations before the aspirant attains the goal. Centuries of continued sacrifices, service, self-purification, suffering, and determined search have to roll on if the aspirant is to be spiritually prepared for the final realization of God. God-realization, which is the goal of the reincarnating individual, is never an attainment of a single life. It is always the culmination of his continued endeavor through many lives. Unintelligent karma of many lives has created the bindings of the individual soul, and it has to be undone by the persistent creation of intelligent and nonbinding karma carried on for many more lives.
–Discourses 7th Ed., p336