Design patterns·The named ways it goes wrong
understanding one method meant opening five files up and down the hierarchy, and then going back up again.
Yo-yo problem
Also calledyo-yo problem of inheritance, hierarchy scrolling
The reading cost of a deep inheritance hierarchy, where following the actual behaviour of a call means moving repeatedly between ancestors and descendants. It is the concrete, measurable objection to deep hierarchies — not that they are inelegant, but that nobody can hold one in their head. Flattening and composing is what removes it, at the cost of some explicit delegation.