Wood has some odd behavior. Once a tree is cut down it is not alive, and neither does it need to breathe, yet it does have seasonal shrinkage in certain directions but not others. No shrinkage in the "0" direction (see the top right photo). Maybe a little, .01%, if you want to be exact, but not enough to matter in use. Across the grain in the "1" direction it shrinks almost 10%! And what really makes it difficult is wood shrinks only 4% in the radial "2" direction. These percentages apply to thoroughly dried wood to 6% moisture content. These are just the seasonal movement percentages for dry wood!
Thats why it warps, splits and changes shape as it dries requiring special techniques to build with (as shown in the middle right diagram). That is where plywood has changed the world. The wood plies alternate in direction, and as long as the plies are 1/8" or less in thickness they lock each other down into a stable non-moving sheet of plywood. The diagram at the lower right is courtesy ofwww.lozidesigns.com, specialists in making cool plywood designs.
Why use solid wood if its so tricky to use and costs more as a material? Some of that increased cost is not knowing what you are getting into until you cut it open!
See my next blog post for differences in building furniture with solid wood versus plywood.