Confidence is not a bad thing. When you are good at something, it's okay to be confident about it and not being afraid to succeed.
However, cockiness is not the same as confidence.
When you watch professional athletes compete, there are always those few athletes on the court who get in their opponents faces and talk trash after they make a good play. Some go so far as to talk trash on their opponents during their post-game interviews. The arguments I've heard about this cockiness is this: "I'm okay with cockiness as long as they can back it up."
I think that there needs to be a drawn line between the word cockiness and confidence.
In my mind, cockiness implies that a person knows they're good, and they aren't afraid to let others know. Confidence implies that a person knows they're good, but they are being humble about it. Meaning they aren't purposefully trying to show off how good they are.
Why don't I think cockiness is a good thing? Because it does not make a player look good. If you have ever competed in any type of competition, sports or not, there's a good chance that you've run into someone that was not humble. Did you like competing against that person? Probably not. There's a good chance that the person actually made you angry.
While competing can be fun, it doesn't actually mean anything in the long run. It has no eternal value. Just like everything else here on Earth.
As Christians, it is definitely important to show humility. People don't think highly of people who are cocky. If we are to represent Christ and glorify him in everything we do, then we are not doing so if we don't show humility. People will not see a representation of Christ in someone who is talking trash during a game and talking about how good they are. If you are the opponent of a cocky person, and you know they claim to be a Christian, are you really going to want anything to do with the God that they worship?
That's why it is important as a Christian to be humble. Look at the damage you could do if people know you claim to be a follow of God, but you don't show it. So I leave you with these verses...
"When pride comes, then comes disgrace, but with humility comes wisdom." Proverbs 11:2
"Your beauty should not come from outward adornment, such as elaborate hairstyles and the wearing of gold jewelry or fine clothes. Rather, it should be that of your inner self, the unfading beauty of a gentle and quiet spirit, which is of great worth in God’s sight." 1 Peter 3:3-4
"Pride brings a person low, but the lowly in spirit gain honor." Proverbs 29:23
"Therefore, as God’s chosen people, holy and dearly loved, clothe yourselves with compassion, kindness, humility, gentleness and patience." Colossians 3:12
God bless!