Do you also believe that for someone to gain something, one has to take something from someone else first?
Also, I find it hard to believe that every thing a person wants is at odds with somebody elses wants. That is most likely demonstrably untrue.
It's a generality. It is not precise and there are bound to be exceptions.
But there are plenty of things that you want, that if you get it, is likely in conflict with somebody else. Be it the job you have, the Xbox 4 you just bought, or the political goal that you have that we're not going to discuss that somebody else likely opposes.
As to your first question, something that is scarce and likely valuable like a job is inherently exclusive. Me getting my job meant somebody else didn't get a job (probably not forever, but it delayed their receiving a new paycheck). I'm not taking it from somebody else, but I am depriving them of it or delaying the satisfaction of their want.
Now there's probably tons of examples of things that don't follow that principle. But they're not interesting to the discussion. There's plenty of dirt. Nobody cares if I have 2 fistfuls in my pocket and you don't (and technically, you can't have the exact dirt I have, because it's in my pocket).
The point the guy stuck in a telemarketing job was that my want is in conflict with his want. He's not evil for wanting a paycheck, I'm not evil for wishing all of humanity was free from sales people peddling their wares at dinner time. But clearly, if one of us gets his way (BTW, i'm not going to get my way as it's a ridiculous wish), then the other will not get his way.
I pointed out this dynamic because where someone might be trying to make me be the meanie for not liking a business a person is in because of its negative behaviors, when there's people who don't have any respect for the fact that he hasn't advanced out of said job.
I hope he finds a better opportunity that he'll enjoy. but him doing so means somebody else doesn't get that job.