When we lie, we lose a part of our true self. The more we lie, the more we lose. A person who lies all the time will probably have lost a big part of himself.
What does it mean by losing himself? It simply means that the person will accumulate sufferings in the long run. Which means that he will not just be not happy, he will live with a lot of sufferings.
It does not matter if the lie will bring you a lot of money or friends. Eventually, the fire will burn through the paper that tries to cover it.
But there is a kind of lie that is acceptable. There’s a popular tale of a group of hunters asking a passer-by if he has seen a rabbit running pass him. The passer-by pointed the other way. This saved the life of the rabbit. When a lie is intended to save a life or prevent disaster, it is acceptable, to an extent. But must be exercised with a lot cautious.
And one must be truthful to himself when qualifying the lie as a necessity. If not, he will just be deceiving himself, making himself the biggest fool.