Re: Important! I need to talk about a Hadith!
Peace rabika,
Very good point. Lets say If you wished for something and that’s come true, you feel inner peace, than thanks to Almighty Allah for fullfilling your desire. Your wish, feelings of inner peace, and thanking to Almgihty Allah is already known by Almighty Allah by “Ilm-e-ghaib”. What I want to say when predestined is written, it is wrote in such way where Almighty Allah is all knowing about what, when and how you’ll going to ask a dua from Him.
If you are going to ask Him that He may grant you long-life than ofcourse He knows that. If you are going to ask to be a most pious lady, or richest lady, He already knows that too. Nothing is hidden from Him He is All knowing. But its upon Almighty Allah whether He accepts your dua at same time of keep it for after.
I will give you one more example: When I was given exam of biology, I was very happy b’coz I answered all questions very well and I know that I’ll pass this subject with 90% marks, but I failed. In my second attempt the question was harder but I prayed to Almighty Allah SWT that to pass me at this time. My Dua fulfilled and I passed bio exam in second attempt. But if I think its predestined that either i’m going to pass or fail in that exam than do I need to attend the exam?
Almighty Allah knows that I’m going to fail in first attempt and will going to pass in second attempt. Because He knows that in first attempt I won’t going to make any dua but in second attempt yes, I will do dua. About my both attempts, its also known to Almighty Allah as He is all knowing (ilm-e-ghaib) and whether attending the exams or not and asking dua or not is my ‘free will’.
Now coming to the very valid point and hidden logic. I’ll tell u about myself again 
Mostly at Fajer prayer when I woke-up on hearing Adhaan, I say to myself the Jamaat will going to start after half an hour so i’ll wake-up after 15 minutes. So again I went to sleep and I miss Fajer prayer ba-jamaat. This kind of thought is from ‘Shaitan’ who told me abhi half an hour hy thora or so ja. Here comes the role of our ‘free will’. Almighty Allah is know that I’m going to wake-up at Fajer time but I’ll miss it because He given permission to ‘Shaitan’ that you are allowed to astray my servants. So If I make dua to protect me from evil (shaitan) so I can offer Fajer Namaaz, than if Almighty Allah accepted my dua I’ll offer namaaz. This is how dua works and its depend of Almighty Allah whether to accept our duas or keep it for later. Types of Duas depends.
Hope I cleared your doubt. If you need ask anything else feel free to post here. I’ll quote a narration of Prophet Muhammad 
which will help you more to understand.