Tan Sau There are 2 points often overlooked by beginners when doing Tan Sau.
1 - Do not initiate the movement by opening the elbow joint or moving the hand. This is only for raw beginners. At a higher level, the movement should be initiated at the shoulder blade.
If someone were to grab your wrist, it would be difficult to open the elbow joint or try to move the hand forward. You would be using force against force. But you could easily drop and stretch the shoulder blade to initiate the movement, creating leverage for yourself
2 - Do not simply thrust the hand forward. you must use a spiralling movement. Again, this is consistent with the principle of not using force against force.
The legendary power that is often attributed to Siu Nim Tao and Tan Sau is derived from a "spring loading" of the bones and connective tissue of the forearms through the process of supination (outward spiraling), pronation (inward spiraling) and stretching.