If the weather changes abruptly, from bright and sunny to pouring down rain, you're going to get wet. When something happens abruptly, it is sudden and unexpected.
Almost anything can change abruptly, and it will always take you by surprise, whether it's the movement of a car, the mood of a movie, or the behavior of your dog. If you've ever had a conversation with someone who spoke to you abruptly, you may have found them a little rude. A physical attribute can also be described as abrupt, like when the edge of a rocky cliff drops abruptly to the ocean.