Sitting on an idea doesn’t have to mean literally sitting and staring at the ceiling, thinking about it. It means you have an idea and let it stew for a while, your mind coming back to it on its own while you’re taking a shower, doing the dishes, going for a walk… The idea which never comes back is the one you abandon and would’ve been a waste of time to pursue. The idea which continues to be interesting and popping into your head is the worthwhile one.
When you jump straight into execution because it’s easy to do so, you lose the distinction.