It's not about having seen _everything_ out there, it's about having seen _enough_ to operate at the mental level of the categories they exist in. When you're

It's not about having seen _everything_ out there, it's about having seen _enough_ to operate at the mental level of the categories they exist in. When you're just starting out, learning $foo when all you ever knew was $bar is radical change that upends the world. To the more experienced, learning about the existence of $foo is just another $whatsit with $properties and maybe $novel_feature.