Overstep the mark/line British American phrase
In this expression, the 'mark' may be the line behind which runners stand prior to the race. Alternatively, when a line was drawn in the ground that neither boxer was able to cross, it may refer to boxing matches in the past.
To go further or do more than what is allowed
She will lose her temper, if you overstep the mark.
I shouldn't have overstepped the line, so I hadn't been punished
It is often used in all of tenses.
There is no clear information about the origin of this expression.
White lie
Ken: Yesterday I lost the watch that my girlfriend presented to me. Should I tell her this thing?
Lily: Certainly Not! Your girlfriend will be angry with you. Children and fools tell the truth.