I think from a crewmans perspective, its good to have a mental picture of what you are looking at so far as a load goes.
The Chinook that parked in a hurry in Stanley with chunks out of its blades is a good case in point.
The culprit was a badly rigged 40' ISO. The diference with rigging a 20 and 40' ISO is that 2m extension chains are required on the latter at each corner. This culprit container was rigged sans chains, resulting in the 'included' angle between the roof of the container and the sling stirrup to be too shallow. The load came off the ground earlier than might be expected. This then resulted in a catastrophic sling failure, container getting very wet, and a quickstop by the harbour. This was an incident before we had the luxury of redundant rigging, and all ISO's were single point lifts IIRC.