Tasks
What the task demands
Physical work consumes energy and produces fatigue: lifting, carrying, reaching and holding awkward postures. Manual handling should use the legs, keep the load close, avoid twisting and get help for heavy or bulky items. Physical fatigue degrades judgement as well as strength.
Repetitive tasks cause boredom, muscular strain and loss of attention; performance on a vigilance task falls markedly after 20 to 30 minutes without a break. Variety, rotation and adequate breaks are the controls.
Visual inspection is a perceptual task and its reliability is lower than people assume - detection rates in studies are often well below 100 percent, and fall further with small defects, poor lighting, low contrast, expectation and time pressure. Inspection aids (magnification, borescopes, dye penetrant, good task lighting, a defined acceptance standard) raise reliability; a quick look does not.
Complex systems demand a mental model of how the system works. Automation brings its own errors: complacency, loss of situational awareness, mode confusion and difficulty handling unusual events. Procedural documentation, checklists, cross-checking and a second pair of eyes are the defences.
The nature of the task interacts with the person: a highly motivated technician on a monotonous task is still subject to vigilance decrement.
Traps
Questions may claim an experienced inspector is unlikely to miss a defect - false; experience helps but does not make inspection infallible. Also keep physical load and mental load distinct.
Rule of thumb: for any critical inspection, assume you might miss it - use the aid, the light and the second check.