There are four middoth (i.e., character types) in a man: One who says: "Mine is mine and yours is yours" [I don't want to give you anything of mine, and please don't give me anything of yours.] This is a median middah. Some say: This is the middah of Sodom. [It approaches the middah of Sodom. For if one habituates himself to it, then even if his neighbor benefits (from what he gives him) and he lacks nothing, he will not want to give it to him. This was the middah of Sodom, their intent being to drive others away from them — even though their land was a rich one and they lacked for nothing.] "Mine is yours and yours is mine" — am ha'aretz (an ignoramus). [For he takes and gives equally, and this "settles the land." But he does not (have the sagacity to) know that (Proverbs 15:27): "the hater of gifts shall live." This is the general connotation of am ha'aretz, one who wants to make improvements but who lacks the wisdom to discriminate between what is and what is not an improvement.] "Mine is yours and yours is yours" — a chasid. [He benefits men with his possessions and he does not benefit from the possessions of others. He is a chasid, acting above and beyond the letter of the law.] "Mine is mine and yours is mine" — a wicked one.
Mishnat Eretz Yisrael
Chapter Five has a completely different style. This chapter is entirely aggadic and is in the usual style of aggadot in the Mishnah. It is built upon an order of descending numbers. Numerical introductions have been dealt with in detail in the course of our commentary on Trumot 1:1, Shevuot 1:1, Negaim 1:1, and elsewhere. There is no doubt that the numerical style serves the needs of memorization. However, it is not always only directed at this from the outset. In the case before us, counting represents a principled approach, which we will explain in each mishnah. The aggadot in the chapter are complex and complementary from the storyline perspective. Take, for example, the count of ten miracles that happened in Jerusalem (Avot 5:1): The one who made this count already knew about individual miracles. But he then grouped them together and added that they were ten, a count which symbolizes a complete work. In contrast, the one that counted four character traits in a person (Avot 5:10-15) purposefully gathered four angles, in order to hint that he dealt with all the possibilities about this (with all sides of the square).
All other transgressions against one's fellow man are objectively immoral, except for revenge, which seems like justice. Therefore, 'love your fellow as yourself.' Just like you don't want others to take revenge on you, so you should not take revenge on your fellow, even though you are in the right to take revenge. And so too in all other ways you should love your fellow as you love yourself. And Moses Mendelssohn interpreted it as "You shall love your fellow in all the ways of love that you love yourself," equal in quality of love and not in its quantity, whenever there is no conflict between two beloved things. However, that's similar to the trait of a Sodomite (what's mine is mine and what's yours is yours [Pirkei Avot 5:10]), for how can I benefit my fellow without causing myself loss or effort, light or heavy? For there will always be a conflict between my benefit and other people's benefit, and there is no way to give a perutah to my friend without losing a perutah from my pocket.