1. Our sins separate us from God. Isaiah 59:1
2. Lack of faith. Ephesians 6:16
3. Lack of patience or persistence in prayer. James 1:4
4. Not being shielded with the armour of God ie belt of truth,breastplate of righteousness, preparation of the gospel of peace, helmet of salvation, the sword of the spirit which is the word of God.
I read a testimony of someone who was delivered from being a satanist, and he says, sometimes God answers a prayer and it never gets to its owner because their guardian angel is not shielded at a certain point because the christian did not pray for the armour of God. The devil will fight with that angel, grab that miracle and detain the guardian angel as well. The stolen miracle is what he gives to people that go to satanists for help. The captured angel will be released when christians pray.