The most common area of weakness at club level is probably the endgame; in my experience most club players focus their efforts more on openings which they perceive to be the weakest part of their game. Yet here there is an element of confusion because the definitions ‘opening’ and ‘endgame’ are to a large extent artificial concepts. It would be better instead to define positions as ‘simple’ and ‘complex’ after which it’s easier to understand that the openings will always be unfathomable unless someone first understands the simpler building blocks.
Thus we arrive at the apparent paradox that an immersion in endgames helps players understand the opening better, and the fact that this seems counterintuitive to many means that their entire conception of the nature of chess is flawed. Of course I won’t be able to demonstrate this to anyone’s satisfaction in a short blog post but I’ll leave you with the thought that it’s better to study the endgame.