I can be a really cold-hearted-sonofa...
Without getting too far in to the details, I would identify this quality as both my greatest strength and greatest weakness. Being this way has given me the ability to look at things more objectively, and to have the good sense to go after something I feel I'm worth without being too self conscious. On the other hand, this type of attitude has had serious negative impacts on my more personal relationships.
Similarly, we as a planning profession have the ability to be involved in so many important projects without having to claim responsibility for past and even recent mistakes. After all we only offer options, it is the elected officials who ultimately decide one way or the other. On the flip side, we must constantly deal with the frustration of having little if any control over what will inevitably turn into a train wreck occurring right in front of our eyes. I think one cyburbian actually coined this concept of Planning as "responsibility without authority".
Any other examples out there of a subject's greatest strength/weakness being the same?