Satya

The next of the yamas, satya is often translated as truthfulness. Again, there's the obvious consequences for lying to others - loss of trust, the violence (in the ahimsa-sense) of lying itself, and again, the guilt if one has a developed conscience. And, again, it is not healthy to lie to one's self; in a physical context, say, it would be harmful to injure oneself by overstretching to try to touch the floor for the sake of looking good, when one is just not flexible at all. Or, to not admit the truth and take responsiblity after making a mistake, and thus nothing is learned, and so that is harmful in its own way.

To flip the coin, learning from mistakes by being truthful to oneself, acknowledging and learning from the consequences is a very healthy choice. Back to a more external aspect, while one might argue that to be 'perfectly honest' and flat out tell someone the dress really does make them look fat is actually kind of harmful, it's important to remember that these principles can act as checks and balances on each other. Just as excessive ahimsa can lead to (ultimately harmful) passiveness, or even turn dark and become passive-aggression, excessive satya can be ultimately harmful if untempered by that ahimsa - tempered, it becomes tact, allowing the honesty to be as helpful and healthy as it can potentially be, even in a difficult situation.
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"Do you know what astonished me most in the world? The inability of force to create anything. In the long run, the sword is always beaten by the spirit." - said by Napoleon Bonaparte just prior to his death

Through the Looking Glass