On the note of Euclid's Elements, I took a short course on Plato's "Theory of Forms" when I was just learning to really code and it's what helped OOP click in my head. It's fun when totally random subjects help you get an insight into one another.
Although metaphysics as a philosophical enterprise is highly hypothetical, it also has practical application in most other branches of philosophy, science, and now also information technology. Such areas generally assume some basic ontology (such as a system of objects, properties, classes, and space-time) as well as other metaphysical stances on topics such as causality and agency, then build their own particular theories upon these.":
There's another way : Nominalism, abstract blueprints and concepts don't exist, they are just artificial markers we put on sets of concrete objects to express some degree of similarity. That is, There's no such thing as a 'Tree' in the abstract, there's only the green thing with roots and branches under your house and the green thing with roots and branches under mine, we gave them (and countless other green things with roots and branches) the same name merely to express that we view them as equal under some circumstances, but that name doesn't express anything about the concrete objects themselves, just our brains, each object is completely unique and incomparable to any other in any objective way.
Nominalism is similar to prototypical OOP, there is no such thing as a blueprint, concrete objects spring fully-formed into existence directly from the mind of their creator, or they are cloned from other concrete objects. If blueprints exist at all, they are only external descriptions by us observers to denote similarities: that object has x: and y: attributes and that object also has x: and y: attributes (possibly because it's a clone of the first) so they are the same 'type', but those objects don't 'know' they are the same type (well, they do if they're clones, as they point to the same parent, but whatever), and the universe allows any object to grow and shrink and morph independently of any other, similarities are imposed/discovered solely by observation from the outside.
*:This principle might be violated in dynamic object systems with sophisticated meta-object protocols, as the blueprint itself is just an object that you can manipulate and mutate at runtime with various things not in the static description.
Platonism is like ontological OOP. :D