How can the nucleus be lighter than its constituents?

The fact that the nucleus is lighter than its constituents, seems rather strange. How can whole have a smaller mass components? To get some intuition about how this possible, one look at simpler more familiar system exhibiting same phenomena; hydrogen atom. It turns out true here; atom little bit sum of constituents. This difference corresponds to ionisation energy hydrogen. observation allows simple explanation for possible; destructive interference between electric fields proton and electron causes reduction in field hence contribution from energy. be extended nucleus, thus giving happens. In process, idea classical particles being ball-like objects with localised properties, challenged.