James does not say HOW God gives wisdom. He just states the fact of it. Perhaps some expect God to just miraculously insert wisdom into their psyche like King Solomon. (Where are these geniuses?) That’s not going to happen. Even Jesus grew in wisdom (Luke 2:52). It’s a process, like our prayers for patience. Wisdom comes from thoughts; thoughts come from words; words come from experience; experience comes from practice.
Putting confidence in God is also wise. It is a shift away from confidence in self. The tension between God and self is the ultimate test of faith because each person is always there with himself to challenge whether he will trust in God.
The very act of praying for wisdom produces instant wisdom because it is wise to open oneself up to the possibility of receiving wisdom. The act of doubting that God will give wisdom is itself unwise because one closes oneself off to the possibility of receiving wisdom, which, in and of itself, is not wise. It is wise to desire wisdom.