People can succeed (and fail) with all sorts of abdominal training programs. Besides, great abs have been found on many people that train them religiously each day, but better abs have been found on athletes that do no formal abdominal training at all!
The most important factor in developing eye-catching abdominal muscles (the “6-pack”) is decreasing the body fat in that area, plain and simple. As for training techniques, almost everyone should train this area as you would any muscle group. Why spend 20 minutes per day doing endless crunches when 5-10 minutes every other day (or less!) will accomplish the same results? Only athletes (or back pain rehabilitation patients) may need additional abdominal work to assist their core stability in sport (or everyday function).