What are the most critical factors to focus on when learning to master high-speed descending on a bike, and how can riders effectively balance the need for speed with the need for control and safety? Are there specific techniques, such as body positioning, braking strategies, or line selection, that can help riders build confidence and skills when descending at high speeds? Additionally, what role does bike setup and component selection play in high-speed descending, and are there any particular features or technologies that can enhance safety and performance in these situations?