Here is a quote from Ammon, one of the sons of Mosiah, after his mission to the Lamanites:
10 And it came to pass that when Ammon had said these words, his brother Aaron rebuked him, saying: Ammon, I fear that thy joy doth carry thee away unto boasting.
11 But Ammon said unto him: I do not boast in my own strength, nor in my own wisdom; but behold, my joy is full, yea, my heart is brim with joy, and I will rejoice in my God.12 Yea, I know that I am nothing; as to my strength I am weak; therefore I will not boast of myself, but I will boast of my God, for in his strength I can do all things; yea, behold, many mighty miracles we have wrought in this land, for which we will praise his name forever.13 Behold, how many thousands of our brethren has he loosed from the pains of hell; and they are brought to sing redeeming love, and this because of the power of his word which is in us, therefore have we not great reason to rejoice?(Alma 26)
The green text means that he is talking about himself and/the others with him. The red text is when he is talking about Jesus Christ. As seen by looking at the green text, he expresses both humility and confidence. He says "I do not boast," "I am nothing," and "I am weak." But he also says "I can do all things" and "we have wrought many mighty miracles" and "the power which is in us has saved our brethren." How does that work? How does someone who is weak do all things?
Then, by looking at the red text, it's seen that something confident (and green) is never said without red text nearby. Instead of just "I can do all things" it's "In his strength I can do all things." "We have wrought many might miracles, for which we will praise his name forever." Not just "the power which is in us," but "the power of his word which is in us."
Ammon's example shows that confidently talking about oneself alone might be boasting, and our words might be false, but when we talk confidently about the team "the Savior and me" or "the Savior and us," we're not boasting, we're praising God.
The difference is Jesus Christ.
The take-away I get from this is that I shouldn't express confidence in myself alone. When I express confidence, my goal is to include (either out loud or at least in my head [to keep me humble]) an acknowledgement that anything good that I've done only happened through the help of Jesus Christ.
Not only will it keep me humble, I believe it will also keep me happier, because I can look forward to more great things, as I know that Christ will never run out of the power or the love to help me.