It's a psychological affect. Everyone gets the same, but since you notice all those others, it seems you get less of what you are looking for. Then it becomes emotional, strength of memories are based on degree of emotion, so now your mind "remembers" all those others, but not all the ones for your class which are routine/not impactful.
Conversely, if you don't care that you get others, literally don't even notice them, and delight when you get matching ones, it'll seem reversed, but this is unnatural for most to do, and in making the effort can enforce the former.
Nothing like bias, eh?
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