Drive through Brevard, Hendersonville, or Asheville and you'll see plenty of retaining walls that lean, bulge in the middle, or have tipped over completely. Almost none of them failed because of the block. They failed because of what was, or wasn't, underneath and behind it.
The first problem is the base. A wall needs a trench dug below grade and filled with compacted crushed stone, so the first course sits on a level, solid footing. Set block straight on dirt and the wall will settle unevenly the first time the ground gets soaked.
The second problem is water. Mountain slopes send a lot of runoff downhill, and soil behind a wall gets heavy when it's saturated. Without clean drainage stone behind the block and a perforated pipe at the base, that water pushes until the wall gives. Freeze-thaw cycles in winter make it worse.
The third problem is height. Taller walls need setback in each course, sometimes geogrid reinforcement, and sometimes a terraced design with two shorter walls instead of one tall one.
If you're planning a wall, ask any contractor how deep the base will be, what goes behind the block, and where the water will go. We're happy to walk your slope and give you a written estimate, and jobs over $1,000 get 15% off.