Is the lack of success in some life matters, and the accidents and problems caused by humans, predetermined in the Preserved Tablet, or are they a result of negligence or lack of attention? And should one not grieve or regret what has passed, or say "if only" in such situations?

Allah is Wise and All-Knowing; He tests His servant to elevate their status or to expiate their sins. Therefore, the servant must have faith and submit to His wisdom, for all His decrees are good. Belief in divine decree (qadar (definition)) does not contradict taking means to repel evil and attain good. Among the most important of these means are ruqyah (definition) (exorcism/incantations), supplication (du'a), and seeking medical treatment. Do not dwell on the past or grieve; instead, take the means of healing and consult doctors while continuing with ruqyah and supplication.