When you're thinking about person 1 and eventually send an SMS to person 2 about person 1... think while sending the SMS, so you don't send it to person 1 by mistake...
An example of this situation would be to be thinking about choosing a present to your girlfriend, writing a message to a friend of yours asking what he thinks about it, and sending it to her by mistake.
This is just an example situation, of course; not that I've done it or anything...
At least, not that I've done it too many times...
