I realized it with the Falcon Heavy test flight. Watching the dual boosters come in for a synchronized landing back at KSC with the center core almost landing

I realized it with the Falcon Heavy test flight. Watching the dual boosters come in for a synchronized landing back at KSC with the center core almost landing on the ASDS (which though that was a failure on the day, SpaceX can do reliably now) was the moment where I realized it.