A strong sense of confidence is important in any leader. Confidence is a thoughtful combination of multiple things: it's a recognition of your own strengths with a healthy dose of self-assurance that you are both competent and capable of getting the job done. More importantly, confidence is believing in other people and believing that they, too, have the strengths and abilities to accomplish and succeed. This fosters a secure team environment that promotes achieving a shared vision. Arrogance, on the other hand, is alienating in any professional environment. It sends the message that you are the only one with the skills and the ability to execute a job. It says you are past teaching and have nothing else to learn, either from others or about yourself. Arrogance communicates that you are resistant to teamwork and shared success.
Leaders take note: your superior technical skills are not enough and believing that they are will trap you. By understanding the difference between confidence and arrogance it allows you as a leader to always be a step ahead while serving as a friendly reminder to keep your ego in check.
Leading people to a common goal and conveying a vision with clarity and encouragement (especially in uncertain times) requires confidence. A healthy level of it can make you seem more competent and believable, especially when you can acknowledge your limits. Arrogance, however, is over-reliance on oneself expecting blind loyalty and just assuming that people will follow because you are, well, better.
Over-confidence lies more in a weak sense of self-awareness, where the over-confident person tends to take on more things than they can handle and fails to recognize their limits. It can come from carrying over positive reinforcement from one job to another, believing that because you succeeded before, you absolutely will again. This over-confidence can be checked, though. A humbling moment or a self-realization that you may need help with the task at hand will steer that confidence back to a manageable level. But while over-confidence is more of an innocuous misjudgment, an arrogant attitude can leave a leader scrambling behind the scenes, telling everyone he has it under control, when truly he needs to lean on the team members who are fully capable to complete the job. Some may even see a leader's arrogance as an artificial kind of confidence, one that is used to mask an insecurity.
The best way to keep your ego in check is to aim for a self-adjusting confidence. This means that in moving from project to project, you adjust your confidence level to the challenge and task at hand, drawing on your strong skills when needed but also being humble enough to ask for help. And while healthy confidence is always a positive attribute, a confident humility is even better and will only serve to garner you more respect and reinforce your ability to inspire a team.