I agree it is a bit subjective, but also depends on the conditions you find yourself in. For instance...

In most urban settings, I tend to have a routine, or at least a boundary of familiarity with my environment, such as my commute to and from work in New York and thereabouts. Having already worked up several contingency scenarios for that area and probable function, I can be a lot more decisive about when I am put into a survival mode, the criteria are usually fairly distinguishable.

Conversely, when I put myself into an unusual circumstance, say elk hunting in the Colorado Rockies in November, then I must prudently raise my prep level to accomodate the additional uncertainty and risk I've undertaken. This means equipping with more survival friendly gear, brushing up on skills beforehand, and formulating new plans and contingencies while trying to reorient my thinking towards entering the new environment.

The greatest risk is when I am unexpectedly thrust into new situations for which I am unable to prepare specifically for. Global plane flights are problematic, both from the standpoint of the severe limits placed on my gear, and the great variation in what type of environmnet I could be put into should something go wrong. Sometimes you are just not able to adequately prepare yourself, so in times like this you must have your wits about you and excerise that greatest survival tool of all, your ability to reason. It isn't always enough, but it is often going to be all you have.

Almost always these situations are event based. The train into Manhattan breaks down often enough, hunters suffer injuries regularly, and planes crash. Sometimes they can be more subtle, such as getting lost in the woods or losing my wallet or unexpectedly becoming ill, but these are things I can respond to easier, so as you say the most important thing is to recognize that the situation has changed and take appropriate and timely action.