Spencer, there are growth stresses in wood, but there are also stresses from drying:

 

My local millshop is making some s4s runs for a cabinet manufacturer.

One batch is some nice maple, gang rip saw to a cart, to the moulder, to the cut off line, sort and stack. About 10% cull.

The other batch is the same process, but with some lumber they get a good deal on (6 footers, come from tops or bottoms).

They cull about 25% of that.