There is only one kind of certainty

Do you picture a confident person as someone who is highly extroverted, outspoken, and maybe even a touch pushy; a leader; and dominant?
This is what I would call "extrovert confidence." However, there is also "introvert confidence."

While the introvert's approach is not typically spectacular, an introvert with strong values knows what she stands for and is quietly confident can earn respect by good talents, compassionate communication, and a more modest self-presentation. It makes no difference if your personality is more introverted or extroverted; you can learn to be a successful and confident leader if that is important to you.

A more beneficial perspective would be to tell oneself, "I can be confident in my own manner." Carolyn Webb's definition of confidence—"how you feel when you're being your best self"—emphasizes this point.