My job - research science - is definitely one that you have to like to do well in. Two reasons:
1) Outside of enjoyment and interest, there
really aren't many reasons to do this job. Long hours, relatively poor pay, high stress, etc. Almost all of the scientists I know are very, very enthusiastic about the job in comparison to people in other lines of work and it's simply because, if you aren't enthusiastic about it and if you don't love what you're doing, it's an unfair and disproportionately demanding career which you'll want out of asap. Scientists who don't love science do not survive in this field of work. It's too demanding for too little reward.
2) If you don't like doing science, your experiments aren't going to work properly. This is either due to a lack of understanding of what you're doing (since you lack interest in your work), or a lack of care and attention. It's a big, big problem because a), your experiments probably won't work properly if you aren't paying them the proper understanding and attention, wasting your time and resources and b) the experiments that you end up publishing may not be scientifically sound because you're rushing to get them over with. This is an even bigger issue because, when bad results get published, it hurts not only your reputation as a scientist but the entire scientific community that works in your field. In general, a lot of trust is put into published work so when bad work is published, it can cause big problems for people who put faith in it and conduct their subsequent work accordingly. Experiments can get very long-winded and tedious and nightmarish if you don't enjoy doing them, so liking your job is definitely key here.
I also get the sense that you have to like politics and have a certain "fire in the belly" to be US president or a similar position.
Heh, maybe in the US. In the UK, most politicians really don't give two shits about their job. Lots of them don't bother to turn up for discussions in parliament and actively try to cut their own working hours whilst simultaneously increasing their own pay. This goes for our prime minister, too. Every now and then you get a decent one but really, most of them don't deserve their positions of power because they sure as hell don't use them properly.