There is a “theory that effort is not rewarded,” but hard work is always rewarded. Rather, no matter how small an act is not enough to say effort, it will always be rewarded.
It's called “causal retaliation,” and this means that depending on the cause, you receive a reward called an effect. There is always a cause for an outcome. If a cause is caused, there will always be some kind of result. There is some kind of change or effect, as ripples spread when a stone is thrown on the surface of the water.
In other words, the “theory that effort is not rewarded” is not accurate, and “effort is always rewarded, but “it is not rewarded” as expected (sometimes)” is probably more relevant. The problem is not “effort,” but “thought.”
There is probably a problem with “thoughts” that are so arrogant that they dismiss it as “waste” unless it is the “desired” reward (result) for oneself.
Now, as for the “meaning of effort,” which is the idea of the question, particularly “the meaning of effort that failed when failure is not allowed,” there is no “(real) meaning” in everything, whether it is effort or what, if you think about it from a Buddhist perspective.
For example, there is no such thing as an immutable and fixed “meaning” given to things, such as “your life is to become a doctor and save sick people” or “this banana is to please a hungry child.”
Because the meaning is “none,” there are “infinite possibilities.” It's “freedom.”
It changes depending on the person you meet, the person you receive, the passage of time, your feelings at that time, the flow of the times, and all kinds of “relationships (conditions).” This does not mean that the “meaning given to things” changes depending on relationships.
It means that the “circumstances” of people who think about that “meaning” will change depending on the relationship at that time. There is no substance in the meaning, so to put it worse, it's probably the principle of expediency; to put it better, it depends on how the person receives it.
“That effort that failed” also has meaning if that person later accepts that I have grown up because of that time, and if you truncate and accept “that because I failed,” etc., it has no meaning. (Even at that time, I personally feel that there is meaning in terms of “being blamed for that,” but the person himself may not be interesting.)
In summary, hard work is rewarded, and it is human thought that it is not rewarded. There is no real meaning to it, but the meaning is limitless depending on how it is received.