This concept was first talked about in the mainstream largely by Barry Greenstein, in the accompanying website to his excellent book, Ace On The River, where he rates players according to a number of different factors, including their strengths against good and weak players. This is a point many people forget when evaluating plays/players, and one that is crucial to ensuring that you maximise your returns in each game.
The very best players are able to traverse these two skill sets together. Able to both spot and react to good players, while at the same time understanding the key techniques required to extract the most value from weak players.
As an example, some very skilled poker players regularly make severe blunders against weak players, simply because they really struggle to get inside the mind of someone thinking so many levels below them. They second guess the simple plays that win money against weak players, choosing instead to try and make thin bluffs and hero calls which are simply completely lost on players who are not capable of making or reacting to any kind of tricky move. These players can often hold their own in tough games where these moves are crucial to winning, but lose out on a huge amount of value in very weak games, simply because they cannot drop their thinking to the level required.
On the flip side, there are numerous players who are incredibly skilled at beating weak players, but really struggle in tough games. This can take numerous forms, but usually depends on steaming badly or becoming overly reliant on moves which only work against weak players. Both of these leaks have a much lower effect against weak players, as they usually both fail to spot them as well as failing to act upon them. This is not the case against strong players, who will happily run rings around your predictable moves and big tilt problems - a situation that can make you a huge winner in low stakes games against amateurs, but a huge loser against world class players (a player like Phil Hellmuth springs to mind).
The very best players are able to traverse these two skill sets together. Able to both spot and react to good players, while at the same time understanding the key techniques required to extract the most value from weak players. Poker at its heart is a people game, and being able to put yourself in the position of people playing at a much lower standard than you is one of they aspects of the game you must master. Although this can be hard for some people (it is often difficult for smart people to suffer fools gladly), it is fundamental to being able extract the most money from the games around you.