"Humans do a pretty good job", yes but the whatever enables the good performance can also result in 'pretty good mistakes'
Too true. In the course of observing 60 flights 899 deviations were observed, 194 in checklist use, 391 in monitoring, and 314 in primary procedures. Helios would fit right in there as a pretty good mistake as you put it.
https://human-factors.arc.nasa.gov/p...010-216396.pdf