Answer:
the foot-in-the-door technique
Explanation:
"The foot-in-the-door technique" is a technique described in psychology, as agreeing people upon a large thing by agreeing in the smallest thing first.
It is the compliance strategy where people agree to do a large work or request by admitting to a modest request at the initial stage.
One example of "The foot-in-the-door principle" is ---
Asking a person to help oneself in doing shopping for the ingredients for a dish and later on asking the same person to help oneself in making the dish.
Thus the answer is "The foot-in-the-door technique".