Die Daumen drücken

Literally: To press the thumbs

Example: “Ich drücke dir morgen bei der Prüfung die Daumen.” — I'll keep my fingers crossed for your exam tomorrow.

English equivalent: To keep one's fingers crossed

Origin: Two rival explanations compete, from very different eras. One reaches for ancient Roman gladiatorial combat, where a judge's thumb gesture decided a defeated fighter's fate: pollice compresso, a thumb held down or tucked into the fist, signaled mercy, while pollice verso, a thumb turned outward, signaled death. On this theory, today's gesture of pressing the thumb into a closed fist directly preserves that ancient signal for a merciful, favorable outcome. A second, older theory reaches instead for Germanic folk belief, in which the thumb was considered the hand's most powerful digit, a natural "lucky finger" capable of warding off bad dreams and evil spirits; pressing it into the closed fist was thought to physically trap a hostile spirit or demon inside, rendering it unable to interfere with the outcome being wished for.