Right before my friend Cristina moved to my town a few years ago, someone gave her this advice: Say yes to everything you’re ever invited to do.

“Since you’re new in town, you’ll probably get invited to things. But you only get one chance, because if you say no, you probably won’t get invited again. So say yes.”

So Cristina said yes. Over and over. For six months after she landed here, saying yes was her personal mission in life. Would she go to lunch with a bunch of strangers? Sure! Did she...