The thumb is a direct reflection of someone's ego.
If the thumb has no flexibility, meaning it always looks stuck in a more or less 'up' position, the individual generally has an over inflated sense of self. They are not, in general, flexible enough to accept ideas from others, nor are they necessarily willing to compromise on the standards they set for themselves or others.
If the thumb has absolutely no resistance and wants to go down, the ego is out of balance in the opposite way. Meaning, the person is often or can easily be made into a doormat. They have no sense of self, little confidence, and walk two to three steps behind the rest of their crowd - usually with head downcast.
A thumb that is able to be moved into an 'L' shape that has a little resistance, is generally an individual who is in good balance not only with him or herself, but with the world. They are able to listen to others, accept corrections, and have reasonable expectations.
When I was young, my thumb was either too far up or too far down - often in the same week. Then again, I had no sense of self and when I did, it was over inflated.
For many years, I was in balance even if the world around me was not. I knew who I was, what I could reasonably accept from myself and others, and I was reasonable most of the time.
I wish I could post a picture so it can be better imagined, but they have not turned out well.