For example, 150 years ago, radio waves were unknown, but they are all around us, they are fundamental, and when they were discovered, they changed our daily lives.
Another example, imagine a bushman, and asking him if he understands everything. He might say, "Yeah, that's a kangaroo, that's a bush, that's dirt....everything practical, I understand. There are things about God I don't understand, but they are far away." By defining things that you don't understand as 'not important' then you understand everything important by definition.
Another example, this quote from Albert Michelson in 1894, "it seems probable that most of the grand underlying principles have been firmly established and that further advances are to be sought chiefly in the rigorous application of these principles to all the phenomena which come under our notice"
In other words, it is likely that people have always thought these sorts of things, and so far have always been wrong.