The Ancient cultivators called it DAO HEART. However, the modern-day cultivators call it 'WILL'.
They said if one's will is weak or unstable, their foundations become shaken, which in a way makes them inadequate to face those slightly stronger than them.
In most cases, a Void stage expert with a weak Dao heart will fall against an Ascendant with a much firmer Dao heart.
However, if one's will is strong enough or firm, then when against even a mountain, they stand firm, and no matter what, they will never be shaken.
Klaus is a paragon, someone who doesn't even see the heavens as a worthy opponent. So in front of three mere dragons, Klaus stood his ground, and despite the pressure bearing down on him, his will was still strong, so he didn't give in to the pressure.
This shook the hearts of the three dragons, so in a quick pull, they took away their pressures.
In fact, if one were to look much closer, one would have seen a fearful look appear in the eyes of the three dragons.
