This situation didn't arise in the actual game, but it's an important common beginner error and deserved to be on the list.
The first pieces played typically form the diagonals of the board, a kind of giant X.
One of the goals of each color is to cross those diagonals and have more places to play on the other sides of them.
In order to do that, certain squares are critical to fill, as they are the ones that give access to the other side. One term for this is "the gap" ... kind of like a mountain pass.
In this picture, the Red Y "misses the gap" (by one square to the right).
In effect, Red has indulged in another form of self-blocking.
Red needs to ``hit the gap'' on the way up, to be able to play on the top half of the board. The Y seen above fails at this, and it's a big deal. We must remember to hit the gaps. Like this:
Simply flipping the Y piece right to left accomplishes the goal nicely!
That small difference in that play makes a BIG difference in the game.
