The Importance of Interaction in Physics

With one single electron, it's hard to say where it ends. Size isn't something that's inherent to the object. It's about the interaction, which means it depends also on the thing you're interacting with. A neutrino would pass through a cloud of electrons and have a much lower chance of interacting than another electron would. Poken up a pile of electrons with a stick of dark matter, you're going to get almost no interactions.