By relying on Him, you have confidence in yourself. You are guaranteed the support of your Father; one who is infinitely more powerful than you.
However, if you rely on yourself alone, you deceive yourself into having confidence. For by our own powers we can do nothing, but with the Father we can do all things.
Thus, the more you trust in the Father, the more you rely on God, the more confidence you will have. "If our God is for us, who can be against us"?
Relying too much in God is like being in "too deep a relationship with Jesus", or "being too loving", or "being too sinless".
None of the above make sense; and relying on yourself alone makes no sense at all.