In Part Four, why did Hans risk frightening Liesel terribly?

From the text:

“Liesel, if you tell anyone about the man up there (Max), we will all be in big trouble.” He walked the fine line of scaring her into oblivion and soothing her enough to keep her calm. He fed her the sentences and watched with his metallic eyes. Desperation and placidity. “At the very least, Mama and I will be taken away.” Hans was clearly worried that he was on the verge of frightening her too much, but he calculated the risk, preferring to err on the side of too much fear rather than not enough. The girl’s compliance had to be an absolute, immutable fact.