What is the reason for a religious and diligent student failing in their studies, despite seeking Allah's guidance through Istikhara and fulfilling all requirements of studying? And are both failure and success predestined by Allah?

A Muslim must believe that all matters are in the hands of Allah, and that success and failure are decreed by Him, glory be to Him. A Muslim must be strong-willed, seeking help from Allah, and know that Allah has linked causes to their effects, so whoever strives will find. Failure is not a sign of Allah's displeasure, just as success is not a sign of His love. One should benefit from the experience of failure as an incentive for diligence and hard work.