Is it permissible to say, "Perhaps it is for the best," when afflicted with a calamity, or is it obligatory to say, "Surely it is for the best"?

Predetermination (Al-Qadar) is entirely good in relation to Allah. However, in relation to human beings, some of it is good and some is evil. Allah tests His servants with both good and evil. When someone says "لعله خير" (perhaps it is good) upon experiencing something disliked, it refers to good specifically for that individual, not in relation to Allah's creation. The word "لعَلّ" (perhaps/lalla) has multiple meanings, including doubt, affirmation, interrogation, and hope (tarajji), which can sometimes convey certainty and the inevitability of an event.