This quote (I think you all know where it comes from) shows us that complex physical objects are all different from each other. Ranging from very big ones like galaxies, to very small like the aforementioned snowflakes, there are no two identical instances of them. But what happens if we consider really small objects, like atoms? Well, the atoms of one chemical element aren't actually all the same, but they are not all unique either. Every element has several versions called isotopes, which differ by the number of neutrons in the nucleus. So let's go deeper, to the most elementary particles that we currently know, like electrons and quarks. According to our current physical knowledge, the particles of a given type are all identical. It can mean one of three things:

1. There are differences between them, but we can't detect them due to the technological limitations.

2. They have a complex structure, but there is some physical process that makes them all the same.

3. They are very simple objects that are indeed identical, which means we are close to discovering the fundamental structure of the universe.

I don't know about you, but I think option 3 is the most likely one.