Om Swami
Why should I not lie, even to avoid trouble or to impress someone?
Lying weakens your bond with people and with God
People lie to escape conflict or to impress someone, but in both cases the lie weakens your relationship with that person and, most of all, with your ishta, the deity you worship. To attain siddhi without mantra practice, the root is being devoted to truth, whatever happens, so there is no need to lie.
Many times a person lies to avoid conflict: tell a lie, the matter is over, the chapter is closed, we will see about the rest later.