Our human ability to abstract is perhaps our greatest ability. It allows us to look at this, this and this and call each of them "tree". We need it to understand mathematics, science and, well, everything, really.
But it can be taken too far.
Ideas like Platonic Forms are recurrent themes in philosophy. The idea that the abstractions are more real than the things that they represent. This is, perhaps, the greatest folly of philosophy.
What exists is what exists. Our conceptions and abstractions are merely tools we use to understand and manipulate reality.