You've had a meeting with your client where you delivered some (or all) of the agreed-upon work. The meeting went very well. The client liked much of what you delivered, but they also want changes. And, they found errors and shortfalls in what they think you should have delivered.
Nobody starts out thinking they will have hundreds of tasks
It happens slowly, just a few tasks added every day that just don't seem to get done. Before you know it you have a behemoth of tasks, seething just under the surface of today's task list