I can't speak to Germany, but in the US saving from a good but not extremely high-paying job over the past few decades, investing prudently but not too conservatively, maybe having a few moderately good stock wins from RSUs/options or otherwise, having bought and paid off a house in a not outrageously expensive area, gets you into that range. Depends of course on how you spend your money, educational expenses for kids, etc.
In any case, it doesn't require winning the startup lottery or having a $400K salary at Google.
ADDED: ~$2m + paid-off house is the sort of range people (typically engineers, non-software) I've had discussions about "targets" with have in mind.
