Very well written article about composition over inheritance in OOP.

Also the introduction example reminds me about a bunch of projects I had to work on:

Alan Kay, the inventor of the term “object-oriented programming”, told a story once during a talk more than 20 years ago. You can build a dog house using only a hammer, nails, planks, and just a little bit of skill. I figure even I would be able to build it given enough time. Once you've built it you've earned the skills and know-how, and could apply it to other projects. Next, you want to build a cathedral, using the same approach with your hammer, nails, and planks. It's a 100 times larger, but you've done this before — right? It'll only take a little longer.

While the scale went up by a factor of 100, its mass went up by a factor of 1.000.000 and its strength only by 10.000. Inevitably, the building will collapse. Some people plaster over the rubble, make it into a pyramid and say it was the plan all along; but you and I know what really went on.