Search on Google for information on how to be less confident, and over 90% of the hits will actually be explaining ways to increase your confidence. This does have its perks. According to research from Washington University overconfident managers are more likely to get promoted. Then, they are also more like to make investment decisions that hurt their companies.
Interestingly, research from the business psychology department at the University College London found that males often compensate for lack of competence by showing more confident behavior. Eventually people are going to catch on to this trend. For those of you that already see the handwriting on the wall, you should study how to become less confident.
The ancient Greeks called overconfidence hubris. Hubris had a connotation of harm to it that is not found in current ideas about overconfidence, which we tend to view as a type of naiveté. But according to laws in ancient Athens, the intent of hubris was to humiliate another to exalt oneself. Hubris was not cured, it was punished. The Greeks had caught onto the idea that overconfidence is harmful. Understanding this is the first step in diminishing it.
Actually realizing the limited amount of control you do have over your environs should put a huge dent in your overconfidence. If you succeed, rather than fail in an endeavor, business or the arts, the chances are that your own ability and hard work had a part, but only a small part, in this result. So, avoid the temptation to blame failure on circumstances, and then turn and around chalk up success to your own ability.
Determining your actual impact means being as willing to listen to criticism as praise. Even if you feel the comments are unkind, you may be able to learn something from them. Research from John Hopkins University indicates that for creative people innovative ideas are often spurred on by criticism from others. Honestly question yourself and listen to others who are not the same as you. This is a way to avoid confirmation bias. If you are only hearing the facts that back up what you currently believe, you will tend to churn out the same kind of information and ignore facts that are counter indications when both should be considered.
Finally, let go of the illusion that the perception of success is more important than actually performing well. Perceptions are based on what others say about you. However, this may not reflect what they actually think. I recall a colleague who always responded to the manager’s requests with an assurance of what excellent manager he was, and how his work would also be excellent. It became evident after a while that excellence was not my colleague’s priority. He actually admitted to me that his enthusiasm was just play acting. But, I didn’t have to tell the manager, who already figure out this. I overheard the manager express his anger, more than once.
Others won’t tell you they know you are faking it. But, they will have less compunction about treating you poorly. When any one climbs beyond their ability on claims that they cannot fulfill, people become increasingly disgruntled with them. Just as praise is higher for the confident person, the fall is father. And, hitting the ground hurts.
Artwork: Detail from Icarus by Joos de Momper
 Goel AM, Thakor AV. Overconfidence, CEO selection, and corporate governance. J Finance. 2008; 63: 2737–2784. doi: 10.1111/j.1540-6261.2008.01412.x
 Chamorro-Premuzic, T. “Confidence: Overcoming Low Self-Esteem, Insecurity, and Doubt,”
 Johns Hopkins University news release, August 21, 2012, Don’t Get Mad, Get Creative: Social Rejection Can Fuel Imagination, JHU Carey Researcher Finds
 Russo, JE. Schoemaker, PJH. and Russo, EJ. Decision traps: Ten barriers to brilliant decision-making and how to overcome them, 1990