Maybe luck is a little involved there so that there are some people who have worked hard but did not get the results as expected, but I think when you have tried to step then at least you will get an experience that will be a lesson when for example your hard work does not achieve success. Like a group of people in your area that you have mentioned who have worked hard but are still in a low situation in life, but I think I will not conclude everything too early, remember that there is no measure of the length of time a person must go through, and that means that maybe the group of people you mentioned are those who are still in the process of achieving something big and proud, because after all hard work is one of the keys to success.
Precisely, luck is relative and it may work for or against someone depending on the aspect under consideration; however, the input, effort and hard work has a direct positive relationship with the accomplishment of goals. Even when one tries so hard and gets no results he or she gets other things like experience from the efforts put in. Perhaps it could turn into a learning experience which steering changes for the better next time within the strategies and the approaches being used. In many situations, consistency and perseverance are the main factors which may define success, even if there may be years of waiting for the outcome.
One must also note that everyone has our own success story and the period to success differs from one individual to another. While looking at the group of people you named, they may not necessarily get the results they expected, this means that their efforts were not wasted. This process could be a step forward to the achievement process. Sometimes success is not easy and that brings in a very important factor which is tenacity in the face of challenge.
I think everything you said is true, and it can also be a reason why some people succeed and some people end up in the middle of the journey, and actually success is something that can be achieved by everyone, but the problem is not everyone really wants to work hard and not everyone who works hard can continue to be patient in going through the process until they achieve the desired success.
This does not mean that success is only for some people, but success is for people who never give up in working hard and also have extraordinary consistency, perseverance and patience. And also actually failure is not the end of everything, because I often hear people who succeed in achieving their success by first experiencing failure, I think we can use one of the public figures, namely Jack Ma, as an example where he experienced hundreds of failures in the process of achieving his success, but he never gave up and now he has succeeded in achieving the success he hoped for to become a famous public figure because of his inspiring success story journey, so it all depends on yourself.