The bullet was headed straight towards his forehead!
Shen Yue felt a shock within his heart, only to see the ripple about to dissipate.
It's an illusion!
What he is facing is an illusion. The emergence of the bullet is because his thoughts, coloured by Tan Sha, are clashing with those of Butusov. Butusov, the notorious king of arms, not only wants to kill Shen Yue but also Nuanyu. Butusov knows the danger and therefore resists, showing images of attacking enemies in his thoughts.
As a thought flashed in his mind, the bullet disintegrated and diffused into thin air, causing no harm to Shen Yue.
This must be the true meaning of "respond to incoming forces without dwelling on the departed ones."
Shen Yue quickly understood it and gained a deeper understanding of this phrase. The right mindfulness during Zen meditation is not completely unreceptive but has a correct response to the influence of the surrounding environment!