Perhaps the very root of religion and philosophy, is to explain why we regard suffering, ageing, dying, and death (and other such facts-of-mortal-life); to be unnatural, unjust: a violation of 'the natural order'.
Since these aspects-of-life are universals, it would be supposed that Men would just take them for granted - yet that is not the case. They are instead experienced as A Problem.
The 'puzzle' is therefore the combination of degeneration and death, with an attitude that they ought not to happen.
Traditional religions and philosophies (ancient and modern) have come-up with many attempted explanations for this situation.
For example, the idea that death etc. are an illusion (in the eternal, divine, change-less scheme of things); or the opposite idea that because they are real and inevitable, therefore we should not be bothered about them (followed by attempts to 'train' people into this attitude of indifference).
Materialist modernists ignore the strangeness of our attitude - and instead try to cure the problems, by technological means - so that there would then be nothing to worry about.
(e.g. Attempting to engineer no pain, prevent decline, and enable either a quick and painless death; or entertaining hopes that death itself will be abolished... somehow, sooner or later.)
This is the mainstream secular/left/liberal 'therapeutic' idea of morality-as-suffering; and virtue as that which diminishes suffering (and, conversely, sin as that which increases suffering).
But the serious and honest thinker will recognize that the puzzle is deeper; and none of these are true answers.
A genuine explanation needs to explain - and therefore stating variations-upon "there is nothing to explain" (e.g. it's all meaningless random/ determinism) merely kicks the can onto the deeper question of why we should (and so universally) ever have felt there was something to explain...
The major modern 'solution' to this most profound of questions is, simply: not to think about it.
This is an attempt Not to think; by active and powerful distraction; and by destruction of the possibility of thinking; enforced by propaganda and officialdom.
And this is, perhaps, the real and deepest reason for that attitude of total rejection of 'the past' (and destruction of all reminders of the past) which has gathered so much strength over the past few decades; and lies behind our addiction to media and other technologies of stimulus-saturation/ immersion, distraction and intoxication.
Yet this problem cannot be avoided.
It will always be there; and an implicit (lived-by, 'revealed-preference') answer will always be in-place - even when that answer is being-denied explicitly.
Attempting paradoxically to avoid the problem (e.g. thinking about how Not to think) is at the root of much that is most evil in the world; because trying to ignore a real and inescapable problem is itself to affiliate to the powers of evil: the Prince of Lies and his Empire of Lies.
The reason why JRR Tolkien's The Lord of the Rings is experienced by so many people as the most profound of novels, is that (by his own account) it was rooted in his recognition of the centrality of this problem.
One of Tolkien's greatest, though least known, works was indeed addressing this problem directly.
Tolkien himself never could formulate an answer satisfactory to himself - but he recognized that this failure did not make the problem go-away.
My feeling is that it is acknowledging the problem, and understanding what is at stake, that is vital - rather than formulating a satisfactory answer.
Because then we will be in a position to recognize the true and saving explanation when - after death - Jesus Christ will show us the nature of our perplexed condition, and how it can be solved, eternally.
