I fail to see any contradiction. The key to a successful career in the US is to be relentless in the pursuit of a better job than the one you have now. However, do not be too hasty in handing in your resignation when you have received a new job offer. First, see if you can use the new job offer to negotiate a better deal with your current employer. Flexibility, not loyalty, is the key to success.
I think I've seen this cartoon before. I just can't be *completely* sure that the previous one was a Dilbert, but I know it would *not* have featured on XKCD, and *probably* not on UserFriendly.