The sheepdog's major roles are to pick the direction and steer strays who wonder off back into the herd. One point must be made here. Total failure is not total failure. If a solution doesn't work prefectly the first time, students are programmed to feel that they failed. That's not realistic.
Nothing ever works right the first time.
If they can answer these questions thoroughly and in detail, then they will not be failures. They will be like every other engineering design team in history. Getting it right the first time isn't the definition of success. Being able to find the problems and solve them when it doesn't work is the mark of a true problem-solver. The problem-solving process is reasonably standard.