Do people describe you as a nice person? Are you at the point in your career where you want to be? Being nice may be holding you back, but perhaps not in the way you're thinking. You don't have to claw your way to the top, but you need to be aware of how your "niceness" may be quietly hurting you. Throughout my career, I have supervised many people I would describe as being nice -- people who are great listeners, care about those with whom they work, and who may take on additional responsibilities and cover for co-workers for a variety of reasons. These people might be so nice that you wouldn't even want to think of hurting their feelings. How might you do that? By giving them honest feedback on any not-so-stellar aspects of their performance. Over the years, nice people may not benefit from the learning that comes with constructive critiques and get to a point in their careers where they can't go further without addressing the deficiencies. Meanwhile, those whose feelings we're less sensitive to get more honest feedback and are able to address their weaaknesses.
Beware using the negative feedback sandwich approach with nice people -- the compliments may block out the criticism!
See "Tell Me What I Did Wrong?"
http://www.jstor.org/discover/10.1086/661934?uid=3739704&uid=2&uid=4&uid=3739256&sid=21102272989381
