I was considering working with X on a project.  I asked someone who knew us both, "Is it a good idea to work with X?"  This someone replied, "If you don't have to work with X, don't.  I say this as a friend.  Don't work with X unless you really have to."

X is already extremely accomplished, so X doesn't need the extra feathers in X's cap.  If I decide not to work with X, it won't do X any harm.

Does the same apply to Y, though?  Y is not accomplished. In fact, Y is just starting out.  Problem is, I really don't like Y for many, many reasons. The stuff that I'm doing is somewhat related to Y's interests and I feel this sense of obligation or charity to include Y.  Maybe it's guilt--I feel selfish and mean and spiteful by excluding Y, as if to say I don't want Y's career to progress.  At the same time, I really don't like Y's work at all.  If Y were a newbie, then fine, what Y has or hasn't accomplished is understandable.  However, Y is not a newbie. Y has not performed or delivered for someone at Y's stature.  Y has let many opportunities pass by. The opportunity Y has taken, Y has wasted.  I do not want to share the credit with someone who will not perform at the level that is commensurate to stature. What I would get from Y, I could get from a grad student, maybe even an undergrad.  Y brings nothing and gains everything.  So am I wrong to not want to work with Y?