A prayer is a wish. Your wish is actually your prayer. When you pray to God, and you ask to fulfil your wish, you are asking someone else to help you. You are asking God to help you. Now, just imagine you did not ask in a formal way to God to help you, does it mean you have not prayed? No, it does not. Of course you have prayed. Because the same wish is in your heart. Since, it was so important for you, and you probably could not find a human solution, you decided to ask God. But asking of the fulfilment of your wish to God does not make your prayer more powerful.
Then, what is a strong prayer?
There are 2 types of prayer - the 1st is external - you ask external help from someone (God or someone), the 2nd is internal - this is the prayer which rests on your deeds, actions, and karma.
The 1st prayer is weak. You have to depend on someone else. The 2nd prayer is strong, you depend on yourself. You can make it happen all by yourself.
God cannot be understood. An inferior being (human) cannot understand a superior one (God). It's so simple. In our lives, the superior being, God, is the giver of justice in our life. The scale of this justice is our actions. God cannot be unjust. The wrong deeds done by you cannot be undone by mere prayer. Deeds determine destiny. God is forced to do justice. Because those are his rules. A prayer on bended knee is a weak prayer. The prayer you call upon yourself through your interactions with humanity is the real prayer. That is the strong prayer.