Walter Kiechel III, former Managing Editor of Fortune, states a hard truth:
For about five years now, particularly after dinners that featured wine, human-resources executives have been telling me, "We've come to realize we don't really want most employees for the whole of their careers. We want their particular set of skills when we need them — but then things change so fast, we don't need that particular skill set any more." And many of these are companies famous for being good at H.R.
Related to this I've been telling my students, particularly my undergraduates, two things:
1. Almost every employee today has to consider him- or herself to be, at least partially, an entrepreneur. You should be looking frequently over your shoulder for competitive threats and opportunities. You should continually be updating your portfolio of skills and assets.
2. If you don't like this--the insecurity and the risk--do what I do: work for the government. (Well, that may change soon, too.)