How can one submit to God's decree and destiny, while at the same time supplicating to God to avert a decree that has already been written? And does praising God upon the fulfillment of a supplication increase one's hope for the future fulfillment of what one wishes for?

Supplicating for the removal of affliction and the cessation of hardship does not contradict contentment with divine decree. Remembering Allah's bounties and blessings, and praising Him for them, draws the servant closer to Allah and inspires in them a good opinion of Him. Allah Almighty said: (So remember the bounties of Allah that you may succeed); because that increases the servant's love for Allah, their gratitude, and their obedience, and makes them witness their own shortcomings before their Lord.