You have a chunk of money. Do you invest it all today, or feed it in monthly? This simulator races both strategies through four different market scenarios so you can see how each one behaves.
In rising markets, investing everything early tends to win because the money has longer to compound. When prices fall shortly after you start, drip-feeding softens the blow because later contributions buy cheaper shares. Since nobody knows which market is coming next, most people drip-feed — it is far easier to stick to.