Can I flip your analogy to one I think is more closely aligned.
Your builder mate tells you that building a conservatory will add value to your house and make it easier to sell when the time is right. You don't believe him. He's so confident he's right so he pays for the drawings to be done, gets his estate agent mate to value the house with and without the conservatory to prove him wrong. He then shows you. You are amazed and admit you were wrong. You then agree to getting the work done and you hug and embrace and go skipping off in to the sunset together.
Sounds like a condom advert.