To clarify, I am not talking about attribution. When I say "not stay a 0-day for very long" I am referring to the fact that 0-day use by any threat actor is generally going to be very targeted, because the chance of a PSP and/or network tap logging artifacts or alerting the user is extremely risky in regards to potential exposure of the intrusion, causing the 0-day to likely get burned (Since discovery allows for detection signatures and patches to be quickly created, as well as remediations applied to affected systems).