From my personal observations, it seems there are at least two factors that will determine a person’s humility. I believe the two factors both play against a person’s ego to bring that person’s ego to a stable level. The stable ego level is what I call the point where a person feels good about themselves.

1. Relative social ranking

The first one is the perceived social ranking of a person to the public around them. For example, if a person might be more modest about their academic achievements around someone they know to be in Mensa for fear that what they prided themself on will be unsubstantial in the eyes of a Mensa scholar. Thus causing a blow to that person’s ego.

However, on the flipside, if a person feels that their work is highly regarded in the eyes of the party that surrounds them, then they will be accustomed to talking more about it to strengthen their ego.

2. Current Ego level

The second factor that determines someones humility is their current ego level. Someone who is self-confident and ego is above the “stable ego level” does not need to brag to make themselves feel better and thus the person will be more humble about their achievements. They will strengthen their ego even more by _not_ bragging. By playing back into the first factor of humility, a person will not brag because they feel like they’re the “Mensa person”. By not bragging they feel like the highest member in the social group.

If a person’s ego is below the “stable ego level”, then they will be more likely to not be humble to bring their ego up.

At first these two factors may seem contradictory. However, I feel that they are dependent on a person’s current ego level. I think the first factor is for people’s ego levels that are below what I call the “stable ego level”. The second factor is dependent on where their ego level is.

Disclaimer: These theories are based on my own personal observations of how I think, and what I see from the people in my life. I do not have any scientific data.