I've realized that sometimes when I ask a question I'm worried about seeming dumb. Maybe in that moment it's true, maybe not. Often you appear more thoughtful and engaged. Either way, for the rest of the conversation you'll probably seem smarter than you otherwise would. Continuing without understanding, you're way more likely to say something stupid because you didn't understand that thing two minutes ago. But if you retain mastery throughout, even though it may take some questioning to keep on top of things, you end up able to keep up and contribute better. Recognizing that, and that people just like engaged listeners, has helped me ask "dumb" questions more easily.