> It doesn't matter if it's 99.9% accurate, it's the 0.1% failure rate that will prevent adoption.
Perfectly said. I've always thought the same way. Basically, I'd rather not use a "pretty good" auto complete, because "pretty good" usually means it does more harm than good (where harm is providing wrong results or doing anything that slows me down overall).
See: Every phones autocorrect and how much annoyance they cause.
Reliability and predictability matters a lot in interface design