The single most important thing to remember about human resources is that they're human. Yes, they are a 'resource' and, as such, they have some of the same costs associated with them as any other resource (costs of acquisition, maintenance etc.), but because they're human they need motivation.
People only ever do what they're motivated to do. Motivation can come from many different sources - money, job satisfaction, fear, pride etc. - but the best long-term employees will be the ones with the greatest motivation.
Positive motivation works best too. Negative motivation can work (i.e. do this or you're sacked!) but generally you're unlikely to get as good a return as when you use positive motivation.
You can (and many companies do) run a workforce without any attention to motivation and companies will often still be successful, but one wonders how much more successful they'd be with a highly motivated work force. It's sometimes the way to get that extra 10%.