Said of someone who continues to engage in some action or activity after they have no hope of succeeding or are making things worse for themselves. A: "She keeps throwing money away on these failing investments. It's like she can't understand that they're never going to perform the way she wants." A: "Yeah, some people just don't know when to stop." I told him to stop arguing with the boss like that, or he was going to get into even more trouble. Some people just don't know when to stop.