For example, one might say that Germans usually have their main meal - their dinner - at noon, and smaller lighter meal in the evening. That generalization was once nearly true - maybe a century ago, but even then there were exceptions. Now, a growing segment of the population has its main meal in the evening, but a significant percentage still has a noon dinner, so generalizations about this topic are impossible.
The generalization that most German buildings don't have circular doorknobs - having instead lever-like door handles - still holds true, but the operative word there is 'most' inasmuch as a small handful of German architects use knobs.
So cultural generalization - whether about how Germans hold knives and forks in their hand, or which types of water they drink - are ever subject to change over time, and to exceptions at any one time. Beware!
