Explain how React's Reconciliation, Virtual DOM, and Fiber work together.

Imagine you have a Lego mosaic (the screen). Each time you want to make a change, instead of tearing it all down and rebuilding from scratch (which is very slow), you draw a new design on paper, place it next to the old one, circle the specific Lego pieces that need to be changed, and then only replace those pieces. The drawing on paper = Virtual DOM. The act of circling the differences = reconciliation. Fiber is the smart worker: if he is in the middle of changing Legos and the doorbell rings (the user clicks a button), he temporarily pauses, goes to open the door, and then comes back to continue working—without making you wait.