Our Gemara on Amud Beis discusses the concept that certain items are not nullified even when mixed with large quantities.  The standard Torah rule is that a majority of a permitted substance nullifies a minority of a forbidden substance, if they become mixed together. (If there is a transfer of taste in the mixture, then additional amounts are required to the point that the taste of the forbidden substance is no longer detectable, which is estimated by the rabbis to be no more than 60 times. See Shulkhan Arukh YD 98.) 

Our Gemara tells us that certain substances, such as eggs, which are either sold exclusively by number of items instead of weight or volume (Reish Lakish), or can be sold or counted by item numbers (Rabbi Yochanan), are not nullified even in a thousandfold of permitted substance. This is because the manner in which the individual item maintains a particular identity that is distinct from any quantification creates a psychological barrier for the item to become nullified. Think of it this way, a plain ordinary stone can get mixed up in a whole bunch of stones and you won’t see any difference between them. You just see a pile of stones . However, one egg will not necessarily blend in and be seen as a bunch of eggs because each egg is sold as its own unit. 

Of course, it’s hard not to miss the symbolism that an object that counts itself as unique does not become assimilated or lose its individuality, even when there are thousand others. Many of the mystical commentaries noted this and applied this idea in various ways to the counting of the Jews in the wilderness. For example, Shem Mishmuel (Mishpatim 9:14) notes that Hashem counted the Jews after the sin of the Golden Calf, to remind them that they were important and counted. And he says in Mishpatim (14):  Each person is an important individual and a master unto himself who governs his own spirit. This quality cannot be nullified. Shenei Luchos HaBeris Torah Shebiksav Bamidbar Nasso Beha'alotcha Derekh Chayim says it even more directly: 

Everyone should become aware of his personal value by having been counted. He is encouraged to think that everything depended on his personal activity and contribution. This is why the sages have said that a person should always consider himself as if mankind's merits and demerits were in perfect balance, and his very next action would tilt the scales giving him a chance to determine the world's fate. A single good deed by him would enable the world to endure (Kidushin 40).