Another graphic & useful French expression with no direct English equivalent.
"Mettre le doigt dans l'engrenage" means taking an insignificant tiny first step which is going to end up drawing you inexorably into something - usually trouble!
Like saying "Bonjour!" to the 2 Jehova's Witnesses on the doorstep.
Or going the first few meters down an icy black ski-run.
Or opening a jar of Nutella...
Parting thot: "If your parents never had children, chances are you won't, either." - Dick Cavett