Effective communication implies a process where an understanding of a message between a sender and a receiver takes place.
Effective communication requires the sender to know the purpose of the message. This is what we know as <em>principle of objective</em>. The sender must know what he wants to transmit and what he's going to get with it, as a final result. That's the reason why mindlessly communicators regret what they say, because they didn't think it through. They didn't have a <em>clear purpose</em> or <em>objective</em> when they sent their message.