Every smoker is different
If you put two identical smokers next to each other, odds are that they'll cook dramatically differently.
Smoke is an ingredient, not a cooking method
Pitmasters use smoke like a chef uses spice. They never use liquid smoke.
Thermometers aren't that useful
Purists will tell you that it's all in the feel, not the numbers. A brisket might be the right temperature inside, but you don't know it's ready until you can feel it jiggle just right.
Not all wood is created equal
Chopping a fresh piece of wood off a tree is romantic, but you really want that wood to be "seasoned", meaning it's had some time to dry out. The flip is if it's dried too long, it'll burn dark and hot and your meat will taste like a telephone pole.
Not all smoke is created equal
If the smoke looks black, it's not a good sign. You want a nice light grey color that's nearly transparent, otherwise your meat will taste like a different telephone pole.