I think there are two predominant interpretations.
One, "I'm one or more steps away from the edge" - and two, "I'm falling off the edge".
In my own life, I know I didn't know my crisis point til I hit it (went over the edge), but I've known people who will believe they've hit crisis when things have just surpassed what they thought they could tolerate, and they are in that zone where they don't know if the edge is ten steps away, or 20, or one.
It's a hard thing to evaluate. It's why determining if someone is truly a danger to themselves or others takes some finesse, and why mental health professionals often err way too far on the side of caution - or, miss the signs of a (quiet) crisis.