This is a great question.
For starters, I think it is helpful to distinguish between the definition of the word “confidence” as it relates to the world’s dictionary and the Biblical use of the term.
Quite obviously, the secular focus, as you have correctly stated, has to do with self. Whether that is putting our reliance upon chariots and horses (Psalm 20.7-9), the flesh (Jeremiah 17.5), riches (Luke 16.19-31), or any other temporal thing, it makes no difference. All these things are tantamount to failure.
The Biblical use of the terms parrhesia and peitho, to name just a few derivatives, mean boldness and persuasiveness, respectively. The focus in scripture when speaking about our confidence is as it directly relates to the Person, character, work and word of Christ.
In Acts 4.13 we read this about Peter and John before the rabbinical tribunal known as the Sanhedrin: “When they saw the courage of Peter and John and realized they were unschooled, ordinary men, they were astonished and they took note that these men had been with Jesus.” These well educated, well known in society, well-to-do rabbis were completely disarmed, shocked and caught off guard by the disciples’ speech, presentation and confidence. Nowhere in the story is it inferred or implied that the disciples were arrogant, self reliant, or condescending toward their audience. Their confidence and boldness in their God was what was attractive and compelling and the thing that riveted the Sanhedrin and caused them to take note of a relationship. Their relationship with Jesus.
As you know, there are many more verses in scripture that speak of confidence. After looking up the word in the concordance and reading the scripture references, I was struck by how often confidence and humility coexist together. He increases and we decrease. A work of God, to be sure.
May the Lord grow your confidence in Him so that whether in the mundane or the glorious, the secular or the sacred, people in your sphere of influence will also take note that you have been with Jesus and desire that same relationship for themselves.
Grace and peace,