There are a number of board games and video games where you play a character who collects experience points. And once the character has enough experience points, you get to raise the level of the character, picking up new skills and better attributes. Our careers work in much the same way for many: you work your butt off and then you plateau, you get a new job, or position in a job, work your butt off again, and then plateau again. Provided you continue to level up when you're ready, your career is likely to be full of learning and new adventures, just the way it should be. Here are a few ways you can tell that you've earned enough experience to move up to the next level at your job:
You're bored. This one is a no-brainer. Once you've learned everything you can learn, you are likely to get bored, no matter how much work comes through your desk.
Everyone comes to you for advice. Once you start to get good at a position, and you know how to fix the tech problems, who to call to get that one critical thing expedited, or where to kick the juke box in order to get a song to play. You can feel it in your bones and at first, it feels good. This is when it's time, if you haven't yet done so, to start thinking about what's next. Of course, you should spend as much time as necessary the job to fully prepare for what's next on your horizon, and take your queue from others that you're getting good at what you do, so your ego doesn't fool you into thinking you're doing better than you are!
You get frustrated. After awhile, people constantly coming to you with questions will get old. You'll be annoyed at yourself for being complacent, and you'll start to resent the organization, the team, and everyone but yourself. This means that you have stayed too long, and it's time to move on. Don't let yourself start hating your job; that will do no one any good.
People tell you. Sometimes you'll have a manager in another department start trying to recruit you. Or you'll have team members start to point out other positions open in the organization. Either way, if your humility hasn't allowed you to apply for that next job yet, it's probably time to do so once enough people tell you to.
Money. Capitalism means taking a new job that pays more money when you can. You may love your team, the people, the employer, and the freedom often provided to high performers. But after you start to realize that there's much, much more for you in other ways, if nothing else has caused you to move on, cold hard cash is likely to start being thrown your way.
Finally, there are going to be times in your career when you're not collecting experience to level up at work. New parents, those caring for sick loved ones, team members who have side projects, those spending all of their free time out on a lake at a cabin, and so many others are in a state of coasting. And that's fine. There is nothing wrong with pressing pause on a career provided the output at work is what's needed for the employer, provided both the organization and the employee are aware and that everyone is communicating about where you're at. Communication is key. If you see an employee who needs to level up, dedicate time to review that. If you are in need of a level up, talk to your manager, and if necessary start looking for what your next step is, so you can prepare in whatever way you need to.