How is white lie damaging? Someone is chased by a murderer, he hides in your house. The person who wants to kill him asks you if you have seen the man. And you say you didn't see. How is this action damaging, what harm have you done?
How is this action damaging, what harm have you done?

Actions are 3-fold. They are done by body, speech and mind. All actions originate in the mind (Dhp. verse 1-2).
Unwholesome actions are based in the 3 root defilements, i.e. Greed, Hatred and Delusion. All other defilements are variations of these roots.
When one commits an unwholesome (akusala) action, e.g. tells a lie, then one is stiring up/giving rise to defilements and reacting to them. Defilements are one of the foundations for unwholesome actions.
When commiting unwholesome actions by body, speech and mind, oneself is always the first one to be harmed. That is because one must give rise to defilements and react to them, i.e. act on basis of them, thereby harming oneself and setting oneself back on the path.
One is moving further away from Nibbana, when one commits volitional unwholesome actions.
The Buddha was very clear on the destructive nature of lying, even if a lie is merely told in jest.
This can be seen in the &quot;Ambalatthikarahulovada Sutta&quot;. In this sutta the Buddha is giving an exhortation to his son Rahula, on how to distinguish between wholesome (kusala) and unwholesome actions.
The following quote is the Buddha's words on the topic of lying:


Thus I have heard. On one occasion the Blessed One was living at Rajagaha in the Bamboo Grove, the Squirrels' Sanctuary .

Now on that occasion the venerable Rahula was living at Ambalatthika. Then, when it was evening, the Blessed One rose from meditation and went to the venerable Rahula at Ambalatthika. The venerable Rahula saw the Blessed One com- ing in the distance and made a seat ready and set out water for washing the feet. The Blessed One sat down on the seat made ready and washed his feet. The venerable Rahula paid homage to him and sat down at one side.

Then the Blessed One left a little water in the water vessel and asked the venerable Rahula: &quot;Rahula, do you see this little water left in the water vessel?&quot; - &quot;Yes, venerable sir.&quot; - &quot;Even so little, Rahula, is the recluseship of those who are not ashamed to tell a deliberate lie.&quot;

Then the Blessed One threw away the little water that was left and asked the venerable Rahula: &quot;Rahula, do you see that little water that was thrown away?&quot; - &quot;Yes, venerable sir.&quot; - &quot;Even so, Rahula, those who are not ashamed to tell a deliberate lie have thrown away their recluseship.&quot;

Then the Blessed One turned the water vessel upside down and asked the venerable Rahula: &quot;Rahula, do you see this water vessel turned upside down?&quot; - &quot;Yes, venerable sir.&quot; - &quot;Even so, Rahula, those who are not ashamed to tell a deliberate lie have turned their recluseship upside down.&quot;

Then the Blessed One turned the water vessel right way up again and asked the venerable Rahula: &quot;Rahula, do you see this hollow, empty water vessel?&quot; - &quot;Yes, venerable sir.&quot; - &quot;Even so hollow and empty, Rahula, is the recluseship of those who are not ashamed to tell a deliberate lie.&quot;

&quot;Suppose, Rahula, there were a royal tusker elephant with tusks as long as chariot poles, full-grown in stature, high-bred, and accustomed to battle. In battle he would perform his task with his forefeet and his hindfeet, with his forequarters and his hindquarters, with his head and his ears, with his tusks and his tail, yet he would keep back his trunk. Then his rider would think: 'This royal tusker elephant with tusks as long as chariot poles.. .performs his task in battle with his forefeet and his hind- feet... yet he keeps back his trunk. He has not yet given up his life.' But when the royal tusker elephant...performs his task in battle with his forefeet and his hindfeet, with his forequarters and his hindquarters, with his head and his ears, with his tusks and his tail, and also with his trunk, then his rider would think: 'This royal tusker elephant with tusks as long as chariot poles... performs his task in battle with his forefeet and his hind- feet... and also with his trunk. He has given up his life. Now there is nothing this royal tusker elephant would not do.

So too, Rahula, when one is not ashamed to tell a deliberate lie, there is no evil, I say, that one would not do. Therefore, Rahula, you should train thus: 'I will not utter a falsehood even as a joke.'


-- MN 61 Ambalatthikarahulovada Sutta, p. 523, Bodhi Translation

For further information on this important sutta, there are 2 audio Dhamma talks available.

First one is by Ven. Bhikkhu Bodhi and can be found here.
The other is by Ajahn Brahmali and can be found here.

If you have any questions to what I wrote, let me know.