Why: Krishna now describes the time at which yogis depart, either to return or not to return, naming this as a real, structured teaching about departure rather than something arbitrary or unknowable.

In life: even genuinely mysterious transitions in life, endings, losses, major changes, often have more discernible structure and pattern to them than they initially appear to have in the moment.

Teaching: when facing a confusing transition, look for whatever structure or pattern might actually be discernible in it, rather than assuming it's entirely arbitrary or beyond understanding.