As far as I'm concerned, the following is a basic fact: I lie to my friends; we all do. I therefore, expect that my friends are and will lie to me.
Most of the time one of two things happens:
- You know your friend well enough to know that they're lying, know why they're lying, and accept as part of the tacit agreement of friendship that you do not call them out on it, engage them in their lie, and file away the different meaning in your head for actual later use.
- It's one of the millions of trivial little every day lies we all tell constantly that are so inconsequential you can't be bothered to spend your time working out whether they lied or not and don't even bother to file the information in the first place.
Either way life and friendship goes on much the same and everyone hides each others failings and flaws for each other because otherwise we all go insane.
But sometimes, your friend tells you something, and as hard as you try to analyse it, you cannot work out whether that's the truth or not. Both options are reasonable, both options are valid, both options could be successfully argued both for and against. Even sitting there and going over it and over it in your head in twenty different ways, you come to the realisation that either you don't know your friend well enough, or it's entirely possible they lied to you.
Worse than the lie itself, worse than the act of lying, is the fact that they might be able to lie to you and you might not know it.