Exactly. This is why I don't follow the hypothesis that we're witnessing a crash
due to unhealthy economic indicators/behaviors (debt ratios, QE, interest rates, etc). Of course those things matter, and they certainly suggest the economy is in bad shape (or at least on some pretty intense life support), but they don't seem to trigger crashes by themselves - the indicators and alarm signals have been painfully obvious for years now, and the market should have already taken them into consideration (at least to some degree).
As you say, we can't predict future crashes or the circumstances that trigger them, and I'm not entirely sure we've seen the trigger for a crash now. Perhaps we've set ourselves up for one, but it's doubtful that the indicators themselves will "pop the balloon".
In personal finance, you can use a variety of tricks to hide your bad finances for a while, but it's not usually your debt-to-income ratio (or any other technical indicator) that triggers bankruptcy; more often than not, people keep digging themselves deeper until the bank actually knocks on the door to repossess the house. Governments have historically shown that they can keep the game going far longer than any bank might allow (there are no real terms attached to their debt when they can literally print their own money).
We probably won't know the trigger this time (or any other time) until a collapse is already well underway, if it's indeed happening.