The psychology of humility. Why do we not value our efforts? This question has crossed my mind a few times, and quite recently on reflection it came up again.

Why is it that we rarely value the worth of our efforts?  

By this I mean, why do people often have difficulty in valuing their own work, contributions, sacrifices and in many cases, themselves. Yet, many are quick to praise similar work, contributions and sacrifices of others.

An example is that I don't see my work as a teacher as being of any value, I am not really fussed about my PhD and the published papers,  don't accept compliments well, and even (as some may have noticed) don't feel that I am a particularly good contributor here or on my other SE sites, and as for my own self-value, I literally don't think about it.  But will seek to praise others on their good work etc (note, this is strictly an example)
According to this article, jealousy may cause a person to view themselves more as the person he is jealous of. So if you work hard, write great papers, etc. you may be jealous of another person who has similar attributes. Thus you would view yourself more like him. 

Also in social comparison theory there is the idea of upward and downward social comparisons. If you compare yourself to someone who similar to yourself or more "fortunate" than yourself, you will feel bad. On the other hand, if you compare yourself to someone who is less fortunate than yourself you will feel good. This is why facebook often makes people feel bad about themselves. They see people with trip photos and smiling photos and compare that to their "boring" lives.

Source

Changing Me to Keep You
State Jealousy Promotes Perceiving Similarity Between the Self and a Romantic Rival