Why cars break down ?

Nothing lasts forever; any car eventually will start having problems. However, while some cars may provide you with few hundred thousands miles of trouble-free driving, others start having problems from the beginning. Why there is such a huge difference?
Sometimes cars start having problems after accidents. Sometimes it may be a factory defect or design flaw. Heavy conditions like, for example, driving only short trips without letting the engine to warm up fully also make the engine life shorter.
Corrosion is another factor - for example, park the car for a few months in place with high humidity and later it will probably have more problems than the vehicle driven all this time on daily basis.
Yet, lack of maintenance is one of the most often reason for a car to break down.

Poorly-maintained engine

Well-maintained engine

Here is a visual example:
Compare these two images: the engine on a top photo hasn't been maintained well. Looks like it the engine oil hasn't been changed for long time. This engine has relatively low mileage and already needs serious and costly repair. The engine on the lower photo has been maintained well. After 175,000 miles (281,000 km) it's still in a very good condition, and needs no repair at all. Can you see the difference?
So, what's most important to keep your engine in a good shape?
- I guess, I won't say something new stating that regular oil changes is most important factor to keep the engine running. If you do it more often than suggested by manufacturer's schedule, that's even better.
- Avoid overheating the engine
- Changing spark plugs, air filter, timing belt and other items from maintenance schedule may save you from costly repairs.
- Fix any small problem right away before it causes a serious damage.