And that, or course, is perfectly doable, and is done all the time. Not perfectly, but good enough. However, that's not generalizable to any other particular case. You always need to consider time, processing, storage, network constraints, what does "good enough" mean, and gobs of other stuff. That's the whole point in saying "you can't guarentee deliver-once"--you always have to say "it depends, and depends on what you can settle for."