It's a pretty good choice, one of the rarest things you can have. If someone's loyal then you should never push them away, the problem is that true loyalty is really hard to come by I think.
Reliability.
I know it's not the most exciting answer, but some people are very inconsiderate and don't keep commitments. If you say you're going to do something, do it. If you can't do it, don't say you can. So it's a bit like trustworthy.