influence

AssalamuAlaikum,though I never doubted the efficacy of Dua'a and make it often, lately I have been wondering about the link between Dua'a and our pre-destined lives. How can we completely reconcile the two concepts - does God alter what has already been written in our fate, if we make Dua'a? Isn't it true that what has already been destined, will occur no matter what? Could you shed some light on this for me? Thank you very much.

Dear scholars, As-Salamu `alaykum. Why do not we see any difference to our lives despite that we perform Prayer and other acts of worship in Islam? Where is the defect? Can you please shed light on this critical issue? May Allah bless you all!