It could be that your subject line didn't catch their eye and they didn't open the email. Or they might not have had cash the week you sent it out or mailing list maybe your email didn't make it through their spam filters. The point is there are a million reasons why your readers may not of jumped on your offer the first time you sent it out. And that is the whole point of this lesson. It takes more than just the initial "offer" to make sales.
And if you're not willing to go this extra step, believe me, someone else will! Take a chance. Send out a couple extra emails to your customers/subscribers. The worst they can do is delete it, or unsubscribe. In which case, you stood more to lose mailing list than gain from an unresponsive or uninterested subscriber. Whatever you decide on when to send follow up mailings, it's a good idea let your subscribers know in advance to expect these types of commercial mailings from you, and approximately how often they will receive them.
Now let's take a minute and refer back to the lesson one of this series. If you'll remember we talked about auto-responders and how to use them mailing list to build your list. Now that you know you need to have a follow up system why not take the time to write up several follow up emails for the product that you are promoting and plug them into your autoresponder.