Two kids got a pair of Walkie Talkies, a small two-way radio. They are playing outside, in a large area. They soon realize sometimes the sound is not good, but they keep playing and enjoying when they work.
Airport's control tower use a similar system to talk to airplanes. However, in this case, receiving the right information is really important, so there are agreements in place to get rid of these problems. When an order is given from the control tower, the airplane must not only say they have received it, but also say it back to make sure it was correctly received.
Both TCP and UDP allow two parties to talk to each other, but TCP allows the sender to know that the information was sent completely and correctly.