When you are merely a "lowly employee," you may have dreams of being the boss. You may figure, I have what it takes, or conversely that you can do a much better job then your current one and by all means, if you have it in you, go for it, but also realize that in many cases, it may be a case of you thinking that the grass is always greener on the other side, when it's really not.
1. You're in charge...of everything
Yup, there is no one else you can lean on. You're it. That means every mistake you make as boss is on you and since you are tasked with being the boss and are expected at all times to basically know how to do your job and do it beyond well, when you falter, the outcome for you is a lot harsher than it would ever be for that of just a regular employee. Also know that even if you have a so called job description that tells you, you are responsible for only x, y, z, often times that is thrown out the window and what you're really responsible for is everyone and everything that comes and goes and goes wrong in the building and everyone will let you know that at the most inopportune times.
2. Everything is your fault (even when it's not)
Part of being the boss is that you are responsible ultimately for a lot or all of the actions of your employees. Is it unfair that you may be blamed for what an employee does on your watch, YES, but the reality is, they ARE under your watch. You are responsible for managing them and making sure they do a good job as part of your team, and when they don't, if you don't take swift action, there may be serious consequences to your own employment with that company or reverberations in the work place for having staff that do not meet company standards.
3. You're not "one of the gang"
Do not for a second believe that you are one of the gang especially after you move on up the ladder. Don't fool yourself into thinking that you and your employees can just hang out in the same exact way you used to when you were on the same level. As harsh as that seems, you can get into a lot of trouble in and out of work for hanging out. For example, you go out to drink with what you think is your same crew, and someone video tapes you (even outside of the job), getting drunk and they post it and your higher ups see it, or someone accuses you of playing favoritism, or sexually harassing them, or someone uses the tape for blackmail.
Any number of things can happen, so if you do choose to hang out like that on a a social level with your staff, you may need to consider informing your higher ups prior to and definitely abstaining from drinking or other behavior where you may not be aware of your actions. Also difficult for a lot of people who have moved up the ranks, is you will come to the quick realization that people may not treat you the same because you have become "the man," or "the enemy," even if you are a really good boss. Employees don't necessarily feel comfortable socializing with someone that has the ability to fire them or who can make their work life difficult, or they do not feel free to talk sh*t about others or the job because they don't know if you will use that against them or their other work friends.
4. Everyone is a MF critic
Get it out of your head that you can please everyone. You can't. You give everyone a raise, it's not enough for some people. You happen to have some donuts for the morning crew, the afternoon one feels you purposefully left them out. You give one employee praise, you're accused of favoritism. It never ends. Get used to it. Set the standard, largely based off the company one, of what constitutes as being successful at your job. Is the job of your crew getting done well, efficiently, with few to no errors. Are you superseding or fulfilling your own duties. Are the higher ups pleased with what you have been doing...or is there any validity to what is being said. You have to be able to ignore the BS, but also tune yourself to hearing ways you can actually improve.
5. Be prepared to work all the time
Every person who thinks they can be manager and only ever work from 9-5, needs to have a major reality check. When s--t hits the fan 7 days a week, they can and will call you AND expect you to be there. If you have kids or other jobs or other major responsibilities, do not become a manager or supervisor because you won't last long. It will be hard to take vacations, hard to take time off, hard to have a life depending on where you work. You're always on call, always on duty, always needed to do something on even some of your well deserved off days. Come on early, stay late, work OT, work special events or crunch time days..that's you. Especially keep this in mind if you are trying to climb from one high up position to the next, because someone is always taking notes and saying, well, we had to call you and you didn't respond or you didn't come in, but someone else did.
6.You're bound by the morality clause
An employee of yours may slip up and bad mouth the company or do something sketch and get away with it, but as the boss and manager or supervisor, you are held to a much higher standard than the rest. Know that on and off the job, you are always being watched. Be careful with your social media, like I said early, who you hang out with, and how you represent the company on and off the property. As part of said company if you are caught violating the morality clause, you can be instantly fired, just like that. Make sure you read and understand that thing, because it may come back to bite you in the butt.