(one's) mask slips phrase
One's real character is revealed, which stands in contrast to what they have been pretending
When faced with benefits or difficulties, her mask slipped.
It was only after they got married that his mask slipped.
Be able to understand one's behaviour or character
To reveal one's true beliefs, personality, character, or disposition
Used to refer to a black character in film or literature who often exists to help white characters through the use of magical powers
The verb "slip" must be conjugated according to its tense.
The origin of this phrase is not clear.
Someone who is totally bad at doing something.
Mary really can't sing for toffee.