My best friend Delia and I repeat this wise adage over and over again. It fits so many situations, as in:
"X and I had an amazing date tonight -- we had a great time, and amazing chemistry. But you never fricking know... he just might fall off the face of the earth." (oh man, if I had a dollar for every time this happened...)
"I really didn't feel like going out tonight -- but you never fricking know -- gotta give John a chance, he could be a great guy."
"So I didn't get a vibe from Mike on the phone -- but you never fricking know -- maybe we'll hit it off in person." Oh, but in this case, I DO fricking know... no vibe on the phone always equals no zest in person. It's been proven by scientists. And me.