SHTF is an umbrella term. Unfortunately, potential causes and effects of potential scenarios encapsulated by this term are so broad that many resort to coloring the magnitude of danger with TSHTF, WROL, TEOTWAWKI, etc. Worse yet, it is often difficult to decipher if the author is addressing regional catastrophe (Katrina), national (Argentina) or global (solar EMP).
The truth is - men always expected the end of days are near. Historic records show that all civilizations Egyptian, Greek, Romans, etc, widely believed that time is just about to run out, typically in the next 2-3 years. Our country has a long list of characters that predicted the apocalypse is just around the corner. Sometimes these people are successful in convincing others to abandon their normal lives and “head for the mountains” to prepare. Sometimes even mass suicides are part of the deal. Every decade or so, they come up with a new reason why SHTF is just about to arrive. So many reasons have been invented, that defining the actual meaning of this term is impossible.
However, these days, the most often interpretation of SHTF meaning is the cartoon world of The Road. The methods of getting to that world have recently changed. Few years ago when the prices of gasoline kept climbing every week – it was Pick Oil. Then EMP, which is still one of the favorites. However, today it is mostly dollar collapse. Mind you, most of these survivalists failed high school math, never mind undertaking any economic studies. Most have no idea what EMP is or the fact that each has different (almost unique) parameters. Or that most will not even stall your running car let along kill all modern cars.
Having said this you might get an incorrect impression. I do strongly believe in independence and self reliance. As such I do believe in having food, water, meds, heat, ammo, etc. I know for a fact that our utility infrastructure (water, sewer, roads, bridges, electrical grid, etc.) is collapsing and requires huge investment. As someone who does economic and financial research for living, I do believe the current economic climate, our financial condition, and government policies are very unnerving.
Rather than attempting to define SHFT, you might find it useful to identify and categorize various emergencies that you might face. Doing so should help you to prepare individual emergency based tactical strategies and needed resources. It should also help your mental preparation so that when you see signs of one of your prepped for scenarios come to life – you be able to immediately identify it and know exactly what to do.