A person must be able to endure what he clairvoyantly observes and this encompasses such strength of character as but few can imagine. For example: If you are not clairvoyant and tell a lie, it is wrong. However, if you lie when you are clairvoyant you will see the lie becoming visible and what that means on the astral plane. Then you will understand why it is said: to tell a lie is murder. It is like this – suppose you have seen an event, you have formed an idea of what has occurred but what you subsequently tell about this event is incorrect, made up or untrue or something to that effect. Then there will emanate from this event the reality of what has occurred while from you there will stream the incorrect account – this results in a collision and it causes a terrible explosion; and every time you do this, you attach a horrific creature to your karma, where you will not be liberated from, until you have corrected the lie you have told.
Source (German): Rudolf Steiner – GA 98 – Natur- und Geistwesen – ihr Wirken in unserer sichtbaren Welt – Vienna, November 5, 1907 (page 25)
Translated by Nesta Carsten-Krüger