The Bible says, “Forget about self-confidence; it’s useless. Cultivate God-confidence,” (1 Cor 10:12, MESS). Does this mean it is ok to be negative and walk about with a “can’t-do spirit?” Of course not. In the context of where this Paul is speaking, he is telling us to "trust God" rather than our "selves." This Scripture is telling us to ultimately remember that it is through God in Christ we can accomplish any task and overcome any challenge before us.
The Bible says, “I can do all things through Christ who gives me strength,” (Phil 4:13). So this means we must first have self-confidence, we must first have the conviction and feel the assurance that God’s word is the truth (John 17:17). Next we must take stock of ourselves as believers and realize who we are--God’s sons and daughters (2 Cor 6:18). This means we have entitlements, inheritance. For he is our Father. Scripture says, “In him we have obtained an inheritance,” (Eph 1:11, ESV).
So once we depend on Christ and have him as our foundation; once we remember that his spirit inhabits us (Gal 3:3) and through that spirit we do miracles and more (Gal 3:5); once we remember that all we need do is to ask him in Jesus name for all that we need and he will give it to us (John 14:14), this is how we cultivate God-confidence. The Bible says, "And my God will supply all your needs according to His glorious riches in Christ," (Phil 4:19). Further Jesus himself says, “For nothing will be impossible with God,” (Luke 1:37).