A friend tells the truth to protect you, to prevent you from making serious mistakes and creating future problems.
An enemy tells the truth about every little error or indiscretion you make to blow it into a big issue in order to condemn you and bring you down. Or they tell a lie disguised as truth.
The difference is, a friend sometimes has no choice but to lie to shield you from immediate danger while your enemy lies to gain an upper hand over you. Sometimes the difference can be very murky. You got to be wise or street smart enough to know the difference between a lie or the truth, a friend or a foe. Otherwise you get ruined by an enemy or run the risk of losing a friend forever.
When dealing with family, for goodness sake, tell your loved ones the truth no matter how unsavory the truth is, especially that which would directly affect them. Otherwise that fact would come back and bite you in the butt sooner or later.
Sometimes keeping quiet about the truth is equivalent to telling a lie. One example is the One Eyed Mum story that recently went around the internet. My opinion is it's melodramatic but not completely unrealistic. Some mothers are capable of such gross silly notions that they're protecting their kids by shielding them from reality. Fact is, they're causing more harm than good.