You posted picture does not make sense to me. You seem to be equating the size of sets with the value of the sets. Sets are, by definition, unordered. Of course, when we discuss countable sets, we are essentially saying we can order the elements in a way such they can be counted. But what do you mean by a count of 2 or a count of 1? Makes no sense. When we discuss counting elements in a set, what we are doing is ordering the elements such that they can be counted with the set of natural numbers. Or to be more precise, a countable set is a set that has a one-to-one and onto mapping from the set of natural numbers to the elements of the set being counted (note: for finite sets, we are obviously not mapping the entire set of natural numbers, just those natural numbers <= to the size of the set being mapped). At any rate, a count of 2 makes no sense.
So, lets rework your example using proper notation and terminology:
{1,2,3,4} != {2,4,6,8} That means the sets are not equivalent, they do not contain exactly the same elements. But, using the correct notation: |{1,2,3,4}| = |{2,4,6,8}| . |S| denotes the size of the set (ie its cardinality). One cannot say {1,2,3,4} = 4. That statement makes zero mathematical sense. One can say |{1,2,3,4}|=4. That statement says the cardinality is 4.
So, then if we extend this sets to infinity:
{1,2,3,4…} != {2,4,6,8…} The sets are not equal, ie they do not contain the same elements
|{1,2,3,4…}| = |{2,4,6,8…}| The cardinality of the sets IS equal, they are the exact same size: countably infinite. The function: f
= n*2, where n >0, provides an exact one-to-one and onto mapping. For each and every natural number greater than zero, I can find exactly one, and only one member of the right hand side set.
There is obviously not a paradox between saying the size of the sets are equal, but the elements of a set are not the same.
And why do we have to agree at all?
Well, I assume you started this thread because you wanted feedback on some of your mathematical speculations. I am trying to help. We don’t have to agree, you can go through life probably just fine misunderstanding of these concepts, provided you do not want to be a mathematician or a computer programmer or you never have to pass a course in college of certain math subjects (eg discreet mathematics).