In React, we try to avoid mutating data structures and instead, treat them as immutable. This means an update to an object or an array should result in a new object or array that reflects the updates we want to make. This allows React to use reference comparison for optimization purposes. We don't always need this, but if we are consistent in treating data as immutable, we can take advantage of that whenever we need it without having to go back and change existing code. In this lesson, we'll see how we can remove an item from an array without mutating the original array.