It's no secret that among a lot of people, it's a fairly common sentiment to regard the managers as overly ambitious people who require to get paid a lot for no reason and at the same time are of questionable value to the organization (as opposed to, say, engineers, that are doing the actual work). I don't have any desire to argue for or against this position tonight. Rather, as someone who's currently (gradually) transitioning from being being purely an individual contributor to the more leadership oriented roles, I've found that there are a few skills that seem to be very difficult to truly master for a lot of managers. I feel that it might explain, at least to a certain extent, why the (good) managers are so much in demand, and are often worth a lot to the organizations they lead.
1. Learning to let go. Most of us start their careers as individual contributors, which often means that it falls onto us to do the work on the ground and focus on getting all the details right. It also provides us with a reasonable degree of control of the final output (at least for the specific piece we're in charge of). As we advance in our career, however, the situations when we need to rely on the results of the work done by others, be it our peers, or people who report to us, keep arising more and more frequently. Making the mental transition in order to accept and embrace that - learning how to delegate and refraining from the desire to micromanage - often turns out to be extremely hard, and the new mindset might take years to fully master.
2. Learning to control your ego. This is another core issue many people (myself included) struggle a lot with. For me personally, it's not so much about the need to force my views and ideas upon the people around me, but rather about the desire to feel that I'm contributing in a meaningful way. That, however, can be just as dangerous, and again, this is a habit that takes a long time to unlearn.
3. Dealing with the lack of immediate gratification. Finally, I feel that one of the biggest challenges for a lot of people entering management is the reduced amount of immediate gratification that comes with their new positions. I'm not saying that management can't be a rewarding career - it absolutely can and should be - rather, the emphasis here is on the word 'immediate'. This issue is, to a significant extent, tied to the previous points I've made above. When we work as individual contributors, we are often responsible for taking care of specific items on the agenda. We might not have a direct way to influence the agenda itself (and that can be at times frustrating), but at least we can feel good once we are done working on this presentation, or writing that sprint of code.
However, as we find ourselves in a setting that requires managing a team, we often discover that those achievements don't belong to us anymore, but are rather the accomplishments of our team members or subordinates. What that means is that we no longer can feel the gratification stemming from striking a specific thing off our to-do lists, as those aren't not actually our to-do lists anymore. Instead, we have to learn to give credit to the people around us (while still taking responsibility for the failure, if need be), and teach ourselves to focus on the longer-term objectives and the broader picture. This is something that can be incredibly motivating in the long run, but it definitely requires a lot of work to get into this mindset, and is by no means easy to do.