draw the line
Synonym discussion
Sense: idiom/1
All three phrases describe refusing to accept something, but they differ in connotation. 'Draw the line' implies a moral or ethical boundary — you stop because you feel something is wrong, not just inconvenient. 'Put one's foot down' is more forceful and suggests authority over others ('The boss put her foot down and banned overtime'). 'Set a limit' is neutral and factual, lacking the emotional weight of the other two ('She set a limit of two hours for the meeting'). Use 'draw the line' when the refusal is personal and value-driven: e.g. 'I will help you move house, but I draw the line at cleaning your bathroom.'
Etymology
This idiom comes from the literal act of drawing a line on the ground or on a page to mark a boundary that should not be crossed. The figurative use — setting a limit on what one considers acceptable behaviour — appeared in the late 1700s and became common in English by the early 1800s.