Hixee is correct. Stress and durability are factored in, so there probably won't be a design error, but one still needs to account for manufacturer error. The parts themselves could be faulty or have been built poorly or the parts were installed wrong. Since launches like this one are so expensive, precise, and I'm guessing fragile, why not start slow? If something breaks, at least it will be a broken bolt, or a scratch, or a dent, instead of a catastrophic failure(something like Xcelerator's recent accident).