Every chat app makes you invent a handle, and every user has yelled about it. Here's the identity problem underneath — and the collision math that makes usernames unavoidable.
Drag to rotate the crowd. Pink figures share the same display name — only unique handles keep them apart.
What the database actually uses. Never changes, never shown. Messages route by this — not by your name.
The human-readable unique key. Lets strangers find and mention exactly you. Must be one-of-a-kind, hence the pain of picking one.
Pure decoration. Thousands can share it, you can change it hourly. Friends see this; servers ignore it.