Comment by nine_k

> what should be a simple scroll

Because the scroll, as you see, is not simple. The complexity of the real-world scenarios outlined in the post force the complexity of the solution. It may feel that "it's simple common sense" kind of thing, but if you ever tried to implement a simple common-sense thing, you know that it only appear simple.

By the same token, some UX person might read about the mechanics of database transactions with two-phase commits, or about MVCC, and ask why so much complexity exists around what should just be a simple write to disk.

"Reality has a surprising amount of detail."