I am half German and work in R&D … with a bunch of Germans. This gives me the presumption to be able to generalize how German engineers think and why this results in less reliable gear (not only cars) in the so called real world. I also had the pleasure to work with a handful of Japanese, Italian, Taiwanese, Chinese and Russian scientists and engineers, yet let me limit this answer to the two you mentioned.
German and Japanese engineers have one thing in common: they will engineer the shit out of every detail. For EVERY BLOODY component! Thus what they build will fail exactly how and in the circumstances they predict it will. So why the difference in reliability? Are the Germans worse at their job?
No. But they do have a fatal flaw: they are German.
Let me explain.
Germans love rules. They follow those rules. German engineers expect people to follow their rules.
When Japanese engineers go on to design a product they ask themselves: “How will the customers use it? How can I prevent failure if they abuse it?”
The German engineer: “I made this machine and it has to be used in this particular way. If the customer abuses it and it fails it is his fault, not mine”.
And so it is. For most German products, if you use them exactly as the manual states and within the conditions it is designed for it is probably going to last indefinitely. Go outside those limits and you can expect it to fail.
Japanese products on the other hand are going to take a beating well outside specs and ask for more.
Just a little anecdote to underline my point.
We (team: PM, Chemist, fluid dynamics engineer, constructor) developed a particular filter designed for a particular kind of water treatment. We designed it in a way such that it would accommodate about 75% of industrial clients and gave a precise spec sheet that specified the working conditions.
After a month a slightly emotional sales manager came into the lab with a sample container containing purple and one containing clear water. He colorfully explained that our filter turned the water purple and that it was a failure.
We analyzed the clear water. It had 2% more than max manganese content. This caused it to precipitate as KMnO4, which is actually a beautiful beast
When the sales manager came back, he was expecting apologies. He was laughed at, declared an imbecile and sent back to the customer with a recommendation.
We had a good time.
