The phrase "how come" is an informal way of asking "why" something has happened or why a particular situation exists. It is a shortened form of "how did it come about that" or "how did it come to be," and it is used primarily in casual speech to inquire about reasons or causes, often when someone is surprised by something. Unlike "why," which requires a change in word order in a question, "how come" can be used without altering the usual sentence structure, making it easier and more direct in conversation. For example, "How come you are late?" means the same as "Why are you late?" but without the auxiliary verb needed in the "why" question. The use of "how come" is more common in informal contexts and has been used since at least the mid-19th century, though its popularity has fluctuated over time.
