Identity

A man is known by the company he keeps. This seems to be a common belief in almost every society. After all, it is easier to identify a person as belonging to a community than to assess his individual character. AND if you assess a community as having a certain type of character, then you just merrily judge the individual based on his community. Voila, it obviates any need to judge the individual which would be for YOU to do. Instead, you apply a rule book developed by others which allots a certain character to a community AND assess the individual's worth based on the community to which he belongs.

Tiru says here...

Manaththaanaam maandhark kunarchi inathhaanaam innaan enappadun chol - Tirukkural

Though a person's own mind determines his attitudes, his character will be assessed by the company he keeps - Loose Translation

'Inaththaanaam' could well be taken to mean his community which then would translate to the community that he was born in. This then could be Tiru's tongue-in-cheek commentary on the fact that, though people may have their own mind and character, Society will assess them based on their community.

OR, even, a practical shortcut to judging people. Like, on the average, people will imbibe the characteristics of others around them. Thus, someone born and brought up in a mercantile community is more likely to grow up with the knowledge and mores of a merchant. Someone who's surrounded by bookish people is more likely to respect books. And so on. Therefore, a person is likely to be assessed as being a representative member of that community even though he is vastly different.

AND, yes, there is always the company he chooses to be in. Which, perhaps, is a more reliable guide to his character. After all, you'd not choose people around you whom you dislike. Thus, the character of the people around you can be seen as a more reliable guide to your own character. IF, however, you are weak enough to not be able to free yourself from unwanted companions, whose fault would it be if you are assessed by the company you keep, even though your own mind holds different attitudes to those of your companions?

Your company becomes your identity. It behooves you to choose wisely.