I’m having a hard time with your post. This in large part due to the quantity of disagreements I have with what you've written. I’ll do my best to reply, but if the quantity and severity of our disagreements persist, I’m intending to let things be as they are.
Do you agree that trial and error forms a significant part of a living being's activities, and that the process we know as evolution demonstrates a large scale trial and error process? — Metaphysician Undercover
Yes to the first portion, but I have the suspicion that the phrase “trial and error” means different things to us.
To me, trial and error is a method of problem-solving, such that the solving of the problem is its entailed end. It also, in all non-metaphorical senses and applications, strictly applies to sentience: it can only be sentience that tries and sentience that determines failure from success. Trial and error in no way overlaps with unintended, and hence accidental, discovery: if one, for example, accidentally discovers a valuable jewel underneath one’s sofa while cleaning one’s room, there was no trial and error involved in the process; on the other hand, trial and error, because it always seeks an end, is always purposeful, intentional, such that when the problem is solved by this approach, its so being solved is not an unintended accident. For emphasis, although when, if ever, the problem gets resolved via the trial and error processes will be uncertain up until the time of resolution, and although many forms of trial and error utilize haphazard heuristics in the trials toward this end of resolving a problem, the resolution to the problem will never be unintended, hence will never be an accidental discovery in the sense just specified (unless one engages in equivocations of what “accident” signifies). Lastly, neither can a sentient being’s engaging in trial and error processes be devoid of observation (for then one would not be able to discern success from error) nor can it be devoid of doing (for trial and error is itself an intentional doing seeking to resolve some problem) – such that the agent, here the sentient being, which so engages in trial and error must be both doer and observer (in no particular order) at the same time in order to so successfully engage in the activity.
As to evolution being a trial and error process, I then find this to be a fully metaphorical application of the phrasing. Evolution is not a sentient being; and thereby cannot as process of itself intentionally problem-solve anything, much including via any trial and error means. More bluntly, what problem might evolution be intending to solve? This is not to then claim that evolution is not in large part a teleological process, but evolution is not the type of teleological process which applies to the intentioning of individual agents (and only to the latter can trying and failing and then trying again, this with a set goal in mind, apply).
As Aristotle pointed out in his analysis of ends and means, each specific end can be viewed as the means to a further end, and this produces an infinite regress if we do not designate an ultimate, final end, which he named as happiness. So this activity of turning over rocks is like your "happiness", you are fulfilling what you perceive as your ultimate end, you apprehend no reason for this act, or even doubt the possibility that there might be a further reason which you are unaware of, therefore you are satisfied in your acts, and you are "happy" fulfilling your desire. — Metaphysician Undercover
In an Aristotelian model of things, “optimal eudemonia” (what you’ve termed “happiness”) is everybody’s ultimate end at all times – and not just for he who has agreed to uncover rocks for someone else. It will hence equally apply to he who wants the rocks uncovered for his own hidden purpose by the person who’s agreed to do so. And this Aristotelian conception of the ultimate end is only the most distal (distant) telos of an otherwise potentially innumerable quantity of teloi any person might be intending at any given time. And in so being, though one might get closer to it at certain times rather than others (when one is more at peace, or else joyful, for example), this ultimate telos of “optimal eudemonia which can only translate into a perfected eudemonia” is the most unreachable telos of all teloi out there. The most difficult, if at all possible, to actualize. It here drives, or else determines, all other teloi, this at all times, but it itself cannot be obtained for as long as any personal suffering occurs or is deemed to have the potential to occur. This includes some personal interpretation, granted, such as in what "suffering" signifies. But I still find it to be the only coherent way of understanding 'happiness as ultimate end'.
Secondly, why did the person who’s agreed to turn over rocks so agree in this first place? Teleological reasons can range from that of having a gun held to his head (with the person preferring to do so rather than die due to his ultimate end of optima eudemonia), to having been offered a fair sum of cash for so doing (with the person finding the cash worth the time and effort required to so turn over rocks), to simply wanting to make the person who so asks happy (harder to briefly explain but yet a teleological reason). So the person whose turning over rocks isn’t considering “all rocks having been turned” as his ultimate end. At the absolute least, he’s turning over rocks as a proximate end in order to satisfy the more distal end regarding the reason he’s agreed to turn over rocks to begin with – which all then being yet governed by the far more distal telos of “optimal, hence perfected, eudemonia”.
So of course there are (teleological) reasons galore for the act of turning over stones which do not end in the successful act of so turning over all stones in an area. Endlessly ask someone why they did X starting at some concrete doing and you will obtain an endless list of reasons for their doings, much including teleological reasons. (Sure, some such reason that some will give might be the incorrect reasons for their doings - reasons given for things done while hypnotized comes to mind as an example - but this yet presupposes that there are accurate reasons for that which we do, have done, and will do.)