How tricky it can be to capture expressions and the character of a person

Painting people is one of the biggest challenges in artwork, especially when they are up close and you want to capture mood, expression, character and personality. In recent days I have been painting my older brother who is seriously ill with cancer. He is a farmer and I wanted to place him in his natural setting so I chose to place him on the family farm tending to cattle.
This is based on a very strong memory of mine from February of this year - 2011. I visited him and his family and spent some time helping him with cattle feeding. I've painted the picture that stayed in my head from that day and I'm very happy with the scene and setting. I've captured very well his character and personality but I'm not 100% happy that I've caught his mood which is very much expressed in the eyes. In the painting it is a profile view of him so really you can only see one eye clearly. It is his left eye that can be seen in the painting and I'm not totally happy with it. I feel that I have it 90% of the way but the full expression eludes me at the moment. I've decided to leave it for a few days and come back to it again with a fresh view of what I have done.

It is really challenging to capture moods and expressions clearly. The tiniest speck of light or shadow can change an expression in a major way. The slighest curl of a lip can change a smile to a frown. A little wrinkle near the corner of the eyes can convey laughter and good humour. Heavy or light shafows under the eyes can convey energy or fatigue.
The process of doing this painting has revealed a great deal to me.  I will have to come back to this when it is completed.