I'm no expert but there's a difference between the occurrence and effect of specific events and ones level of preparedness for events.
So, if you are late in to work, and its because you had a flat tyre, you can hardly blame anyone for the bad luck of a flat tyre but you can be considered to have been negligent if it turns out you drive around without a spare tyre all the time. People who get burgled are not at fault but those who leave the front door wide open while out would be considered to have been negligent and could forget an insurance claim.
Nobody can be blamed if everyone gets food poisoning but the coimpany can be blamed for not having a contingency plan for the circumstance when a flight creew and cabin crew are not available - the latter being possible due to traffic, weather en route, food poisoning or a lot of other reasons.