We've all trusted a progress bar that said "5 minutes left," walked away, and come back an hour later to find it barely moved. It's not a bug. It's built into how progress bars estimate. Here's the core problem, and it's more interesting than it looks. The lie every progress bar tells A normal progress bar computes ETA like this: "I've done 2,000 of 10,000 items in 10 minutes, so the remaining 8,000 will take about 40 more." That assumes the rest of the job looks like the part...