When does a LIE become the Last Straw ?

How many of you have LIED before ?
I'm going out on a limb and guessing that ALL of you have LIED upon occasion...
So, based on that theory....
When does a LIE become something "other" than "normal" behavior ?
When does Lying BREAK the trust ?
BREAK the relationship ?
When does a LIE lead us to a point of NO RETURN ?
When does Lying actually BREAK SACRED COMMANDMENTS ??
Furthermore...
When is TELLING a LIE OK ?
When is it warranted ?
Necessitated ???
Thoughts ?