...oops.

So this one time when my wife was younger and made mistakes, her dad told her to drink all her milk.  She didn't want to so she poured it down the sink.  He later came back and asked her "did you drink all your milk?" She responded with a big yes!  Well he had seen the milk left in the sink and knew she had lied.  She had nothing to say for herself.
Ever been caught in a lie like that and the only thing you have to say is "..oops".  It can feel really shameful and embarrassing.  I once thought that people wouldn't like me if I told them the truth about me.  I recently realized people like me when I tell them the truth about something awful, than to lie about something good. 

Her dad eventually forgave her : )