The Handstand Challenge can only be completed by people in very good physical shape, and even then, many will not have the strength or coordination to complete it. While this does make the challenge more difficult than others, and thus maybe more gratifying to complete, it also makes the pool of possible participants in this challenge very small. It's highly unlikely that most people could participate in this challenge, which definitely has stifled its popularity. If you're not a super athletic person, this challenge holds no appeal, as physical fitness is really the only thing this challenge is based on. If we consider the amount of people who participate in a challenge and its subsequent popularity to be relevant to the challenge's success, then this is not the most successful challenge.