The other comments are all relevant and very good, but they seem to overlook one important aspect: the company's attitude. What all those comments have in common is that they assume things work according to Tom DeMarco's book Peopleware. I have learnt on my own experience that they don't. I have had the chance to work with 1)poisonous, 2)negative, 3)defensive (see the psychological meaning), and 4)offensive (... no psychology needed here) senior developers. Some nicer/more experienced than others, no doubts, sometimes also due to the lack of communication skills (English is not everyone's first language, and I do understand it). However, these ones were senior due to the number of years spent in the company OR their age. That's why I think that the companies that value someone's skills (I like to see them like technical skills, IQ and EQ) for their promotions are the minority.