I remember Archer years ago on ESPN playing Rob Saez I think? He was having a real bad day, and Archer missed 3 - 4 easy shots. If I remember correctly though he gutted it out and either closed it up at the end or even won the set.
I have matches at home of various players - SVB, Kiamco, etc. - missing almost straight in, 2 foot shots. Similar to what I do occasionally, where I'm either trying to cheat the pocket slightly to get perfect and take my eye off the ball, or simply not paying attention. Difference is I do it every week, they do it like once a year...
I just watched a match on youtube of Shane vs. Pagluyan, from InsidePool, Shane misses 2 easy shots, the last one an easy 9 playing 10-ball, both misses allowed Alex to get back into a match that SVB was dominating. Haven't finished watching (2 hours +) so don't know how it ended up...
So it happens, just very, very rarely.
Scott