Wood is a complex and often perplexing material. Unlike metals and plastics, whose properties are fairly consistent throughout, wood is wholly inconsistent. It is stronger along the grain than across it. It expands and contracts more in one direction than another. Its color, weight, and grain pattern vary not only from species to species but from board to board. To work with wood,and have it work for you, one must first learn its complex nature. You must understand three unique properties that affect everything you build. These are grain, movement, and strength.