Force unwrapping is what it sounds like: you take an optional, and forcefully convert it to a nonoptional. Obviously there must be a valid value at this point in the program, or it will crash. Optionals are useful not only for UIs, but for handling any sort of state where it's possible for something to not have a valid value at any point in time. It just hoists such a state into the type system rather than checking this at runtime.