Wood Grain Alignment
There are two basic wood grain alignments of a board used for board breaks.
Figure 1 is the top edge view a board cut from the center of a tree, where the grains are such that one face is the mirror image of the other. The amount of force needed to break the board will be the same no matter which side is struck.
Figure 2 is the top edge view a board cut slightly off-center from the center of a tree. The left side was closer to the center of the tree than the right side. Since the grain alignment is not symmetrical, on which side should the board be struck?