How can I be responsible for my destiny if I strive and exert myself by all means, yet Allah does not will for me to succeed? And would I then be predetermined to the destiny of failure that Allah has ordained for me?

Whoever takes lawful means, strives diligently, and does not fall short, but success is not decreed for them, then there is no blame on them, neither religiously nor rationally. Rather, this is due to a wisdom known to Allah, and they must submit and be content, in accordance with His, the Exalted's, saying: "No disaster strikes except by permission of Allah. And whoever believes in Allah - He will guide his heart. And Allah is Knowing of all things." However, if the lack of success is due to a sin or negligence, then they are responsible for that, according to His, the Exalted's, saying: "And whatever strikes you of disaster - it is for what your hands have earned; and He pardons much." The servant has a will that is subordinate to the will of Allah, for they are facilitated for that for which they were created.