I had a conversation with a friend today and it centred on honesty and lies. He was of the opinion that lies are necessary every once in a while and are vital parts of the society today.
He prefers to be lied to than be told a devastating truth.
Personally I hate being lied to and prefer the truth no matter the circumstance but I saw reasons for his choice. Knowledge is power and we know people can be intoxicating at times. Immediately an idea or a thought have been placed in your subconscious it plays a role in your discernment and resulting actions. It's not completely possible to discard a particular knowledge that links to your plan.
Source
In summary, trust will be lost and he'd have to let you go.