die Daumen drücken
to keep one's fingers crossed; to wish someone luck
Origin
Origin uncertain; probably from old Germanic folk belief in which the thumb (held as a lucky finger), pressed into the fist, warded off misfortune. Another reading points to the gesture of mercy at Roman gladiator fights.
Building blocks
Words in this expression
Examples
Ich drücke dir für die die !
I'll keep my fingers crossed for your exam tomorrow!