We're straying off the subject a bit here, but the discussion is moving along in a useful manner anyway. Maintenance Departments perform detailed structural inspections in the hangar, in accordance with the maintenance schedule. In critical areas specialised equipment is used, mostly die penetrant and eddy current but sometimes more detailed methods such as thermal imaging tomography or deep X-ray for example. Walkrounds are another matter - a general look around for obvious signs of trouble. Quite often people discover very serious defects on walkrounds but that isn't the objective. When a crew member discovers a serious defect it is only natural to slag off the lazy good-for-nothing grease monkies for not doing a proper job, but that is over simplification. It can be just a matter of how the light catches things.
I recall one engineer who spotted a cracked Main Landing Gear Trunnion in the dark, in the most difficult conditions imaginable using the Mk 1 eyeball and a Maglite. When the aircraft was taken to the hangar, nothing could be seen until the part had been cleaned with solvent and a die penetrant check made. Changing the trunnion took three days and, while the engineer concerned is to be congratulated for his vigilance, it was really a matter of luck that the crack happened to be visible from a specific viewpoint at a particular time and place. The crack was invisible half an hour later, in good light, in the hangar, to engineers who were aware of its presence and location. People do not overlook cracks or other defects on purpose, there are hundreds of ways that a problem can be missed, even by the most dedicated among us.
So, lets all keep our eyes peeled, check and double check and make flying as safe as we possibly can. Designers or Maintainers, Manufacturers or Operators, Aircrew or Groundcrew, we all play our part and all work together to the same end. Please, lets not descend into slagging off each others professionalism. It isn't professional.
**************************
Through difficulties to the cinema