I remember many years ago a friend's father commenting on my PhD by saying "isn't it wonderful to be the only person in the world to know about this thing that you're working on?" That's the moment when you have your unusual observation, something that nobody else has seen before (or at least nobody has published before) and it truly is a wonderful feeling. You rely on your advisor to tell you work to look initially, and eventually you get good at finding those places to look yourself.
As Frank Westheimer once said (paraphrased) "Science starts with an unusual observation. When you have an unusual observation, one of two things has happened: you've made a discovery or you've made a mistake.". That's also an important lesson, and one that formed the core of my PhD.
I suppose this is the reassurance of being educated in the engineering sciences: the results speak for themselves.
I agree this should be the goal, but I’m not sure it’s consistently realized in practice. It seems an awful lot of research is derivative or auto-cited, so I’m not not sure it would fall into the “pushing the boundaries” category.
What's interesting is that the chemical reaction that was described in my paper that I linked elsewhere in this comment section [1] was originally discovered by some Japanese scientists in 1970, and we referred to their work as the "Oka Fragmentation". They too pushed back the boundaries of knowledge a little bit as well and we built on top of that. Also, my paper was arguing against conclusions made by a different team at Johns Hopkins - our work was ultimately shown to be correct as born out by subsequent experiments from our research group and others. So that contributes to the boundaries of knowledge by showing that some other body of work isn't correct. Who knows, perhaps our work will be shown to be incorrect in some future research.
I guess what I'm trying to say here is that it's very difficult to discern impact at the time that you do the research - the impact can only truly be seen through the lens of history looking backwards.