The idiom “draw a line” means to set a limit or boundary on what one will do or tolerate.  It signifies establishing a boundary, often in terms of acceptable behavior or actions, beyond which one will not go. 

For example:

I’m happy to help out with the party planning, but I draw the line at decorating the entire venue myself.

He’s generally quite laid-back, but he draws the line at dishonesty.

Where do you draw the line when it comes to accepting gifts from clients?” 

She said she’d try anything once, but she drew the line at bungee jumping. 

It’s important to draw a line and not let others dictate your actions.

Tradução:

A expressão idiomática “draw a line” significa estabelecer um limite ou ponto final para algo, indicando onde se para de fazer ou aceitar algo. É usada quando se quer deixar claro que existe um limite para determinada ação, comportamento ou situação.