In the Upanisads it is stated that the path of spiritual realization is just like the sharp edge of a razor. The example is very appropriate. One shaves his cheeks with a sharp razor very nicely, but as soon as his attention is diverted from the activity, he immediately cuts his cheek because he mishandles the razor. Not only must one come to the stage of pure Krsna consciousness, but one must also be very careful. Any inattentiveness or carelessness may cause falldown. This falldown is due to false ego.

Srila Prabhupada/ SB 3.26.23-24 purport