Yes, it's definitely a numbers game. It's also an attempt to take a shortcut, and those usually don't work very well. The fact that your buddy has luck with it can be down to all kinds of things, hard to say why it works for him and not for you. But here's what I would do, IF I'd try cold emailing: Use it as a way to start a conversation, not as an attempt to get a sale. I'd never ever buy something from someone who tries to sell me something before he even asks me if I'm interested. Because if he doesn't ask about MY interest, the logical conclusion is that the sale is only in HIS interest, and then the door closes. In other words: cold emailing with an offer is an instant and massive trust-breaker. Imagine you meet a nice girl... do you walk up to her and tell her to kiss you? Of course not. You'd get kicked in the face. But if you have a chat, hang out with her, go to the movies, spend time and have fun... it might just turn out she digs you. Customer relationships are no different. So focus on opening a conversation and building the relationship.

Email marketing, hands down. And not the 'ooh I hope they won't unsubscribe so I'll only email once a fortnight' - no, I'm talking about emailing every single day, sometimes even twice a day or more. The trick is to not bother people, but to be helpful, supportive, inspiring, educational, personable, and fun. Done right, daily emails are massively effective for building relationships with people, turning readers into buyers, and creating brand ambassadors. You might think once a day is too often, but my open rates are a consistent 30%, and people love reading them. They write to tell me that they really appreciate the emails, and even say things like 'you're a blessing in my life' and 'I have breakfast with you every morning'. And, yes, people buy from me as well. See http://martinstellar.com/posts to get an idea of the type of email I write, and if you feel it might work for you but you're not sure how to do it, I'd be happy to jump on a call and answer your questions.

You might like to read Ryan Levesque's Ask Formula. It gives you a system that uses surveys to find out exactly what potential buyers think of the idea, and in doing so you're building a list of already interested, pre-sold buyers.