The teller will usually try to ask you about what the money is for. If they suspect you are under duress (i.e. you are being robbed or under threat of violence) or if you are engaging in illegal activity. They do have training for tellers to try and gauge your physical and emotional state to make sure everything is kosher. You can give them an explanation, or you can be a jerk, either way, there is nothing they can do to stop you from withdrawing 10k in cash. If you requested 100k, that would be a different story, they will try to stall you for a couple of days, but eventually you will get your money.