I'll use a simple example that you might encounter in a game:
class Weapon and class Tool. Weapons are used for attacking enemies, and have properties like damage, range etc. Tools are used for exploring the world: prying open lockers, breaking down doors. They have properties like weight, lifespan, etc.
So what should a Crowbar extend from if the game rules say it can be used as both a weapon, and a tool? To add even more complexity, what happens when you have class RangedWeapon extends Weapon and class MeleeWeapon extends Weapon? The crowbar is both. You can throw it, or beat people with it. So even if you decided it should extend from Weapon, which sub-class of weapon should it extend from?
Instead, it would be better if you could combine different behaviors together. Combine RangedAttack, MeleeAttack, Leverage, and Smash behaviors together into a new game element called Crowbar. There is no inheritance tree or taxonomy to worry about - only discrete behaviors which can be combined in different ways to form new weapons/tools/gameplay elements.