Not one in particular besides the obvious. If it is really fundamental, it is not overlooked.
Every programmer has their favorite tools. Some will use debuggers, others will prefer logging. Some will use class diagrams, others will grep. Some will use IDEs and GUIs, others will use text editors and shells.
Same thing for programming languages, techniques, libraries, frameworks, etc...
So you are very likely to get a lot of answers. It seems that you got an epiphany when you learned about message passing. All programmers had similar experience as they discovered the one thing they really needed.
In reality it depends on the project. Great programmers simply have a lot of experience with many, many things.
My suggestion: continue what you are doing.
Try new things, don't blindly follow other people lists. In the process that led you towards that messaging library, you learned named pipes, unix sockets and shared memories, all useful, and maybe they will be essential to your next project. Had someone else served you that library on a platter, you would have lacked that insight.
Every programmer has their favorite tools. Some will use debuggers, others will prefer logging. Some will use class diagrams, others will grep. Some will use IDEs and GUIs, others will use text editors and shells.
Same thing for programming languages, techniques, libraries, frameworks, etc...
So you are very likely to get a lot of answers. It seems that you got an epiphany when you learned about message passing. All programmers had similar experience as they discovered the one thing they really needed.
In reality it depends on the project. Great programmers simply have a lot of experience with many, many things.
My suggestion: continue what you are doing.
Try new things, don't blindly follow other people lists. In the process that led you towards that messaging library, you learned named pipes, unix sockets and shared memories, all useful, and maybe they will be essential to your next project. Had someone else served you that library on a platter, you would have lacked that insight.