There are various reasons IMO.

19th century reasons:

1. Late unification. Really big topic. Germany became a state in a modern form relatively late, in 1871. Before, there were a whole lot of small states (and some bigger ones). They all shared some cultural, political und legal norms, but they also had great differences. This led to a huge diversity in terms of political culture, for example. Connected with this is that the different german small states also had different religions, varying between Catholicism and Protestantism.

2. Resources. Germany had its own rich coal and metal resources, the most important raw materials of the 19th and early 20th century. This helped a lot during industrialization which started far later than in England. But we had it all here, so we had some advantages.

3. Knowledge. Germany has some of the oldest universities in europe and has a reputation of being the "Land der Dichter und Denker" (Land of poets and thinkers). Some of the most influential thinkers of the last thousand years spoke german (Kant, Marx, Luther, to name a few. Schiller, Goethe, to name poets). This led to what I would call a thinker's circlejerk: Whoever wanted to become a great scientist had to come to germany in some times. This led to more scientists, more universities and so on. Germany had a pretty good science base in the 19th century.

4. Immigration. Germany finds itself in the middle of europe. So whenever eastern europeans wanted to come to the west, they first came to germany. There are various waves of migration from the 5th century up til today and it's totally normal in germany nowadays to have a family name ending with "ow", "owa" or "ic", hinting towards your ancestor's heritage. This led to a huge supply of workforce when the industry needed workers, which led to fully used factory capacities and low wages. This is terrible, the workers suffered, but it made the german economy strong (however it must be said that workers didn't really earn more in other countries).

Now going to the 20th century: 1. To quote the simpsons: "This is germany. It's my best friend because.. Well, geographical convenience." After World War II, the two systems "owned" their parts of germany. The socialistic DDR was bound to the Soviet Union, whereas the Federal Republic was an Ally of the western capitalistic nations. Germany was the designated battlefield of a Cold War turning hot. Also, it was the weakest border of the minds, because people on both sides of the wall were related, spoke the same language, had the same cultural history. This is why it was so important for the western powers to make sure that the Federal Republic succeeded. A western germany struggling to fight starvation would have been a sign of weakness for the Soviet Union and would have possibly driven west german voters towards the communists. So they set up the Marshall plan, didn't look too much into how former Nazi elites continued being Democratic Elites in the 50s and basically did everything to help the german economy thrive.

1. Humbleness. We are the country of the worst crime of all, the Holocaust. We have see just how much evil normal persons are able to do if someone finds the right (or better: wrong) words and symbols. This hasn't started right after the war, but it's been getting better since the late 1970s. We aren't thinking that we are the greatest in the world, but we're trying not to be the worst. We've given up on trying to spread the german spirit throughout the world, we just want to have our decent wealth and that's it. (Keep in mind: This is a generalization, and it's not working in a globalized world, because it's the opposite of a free market capitalism).

2. Political balance. We have a simple left-right political climate. The two big parties were up to the 1990s the CDU (conservative) and the SPD (social democrats). Yup, no postfascists like in Italy, no socialists like in nearly every other country in europe. We were tired of extremists. This also means that there are some useful dumbasses in those parties who try to grab the votes from the extremists like in the CSU (bavarian version of the CDU with some politicians so right wing that would even be ridiculed in the GOP in the USA). Lately, there's been a change in the political climate with the rise of the Green Party (who aren't leftists, in fact a huge part of their voters are value-conservative moderate upper class people who just care for the environment and so on), the ongoing success of the PDS/Die Linke (leftists, the successor of the socialistic party SED which led the DDR) and most recently the Piratenpartei. But all the parties assembled in the parliament accept our constitution and democracy and though there are always some political showcasings, most of them work together really well.

3. Social security. Ever since Bismarck invented to welfare state in germany (in a desperate try to get rid of the SPD, not because he was into helping workers), we've had the thought in mind that if everything goes wrong, society will at least help us stay alive. Yes, there are some problems with the finances and yes, there are in fact some people who just don't want to work (and receive about 500-600€ a month including rent. It's not that much). But we can count on societies solidarity if we fail. This leads to a peaceful society.

This sounds like I'm more than proud of my country, I'm not. There's a ton of shit that makes me want to emigrate. It's just my version of the reasons why my country has succeeded. For today, I'd say the support by the western allies was the most important factor.

tl;dr: Oh come on. Geographical reasons, resources, political culture, a little help from our friends.