Repeating a message makes the message seem familiar, familiarity makes it seem true (thanks to cognitive fluency), and truthfulness — even just the illusion of truthfulness — increases persuasiveness.
It seems too simplistic that just repeating a persuasive message should increase its effect, but that’s exactly what psychological research finds (again and again). Repetition is one of the easiest and most widespread methods of persuasion. In fact it’s so obvious that we sometimes forget how powerful it is.
So if you want your partner to believe that your favorite baby name sounds strong, or intelligent, or friendly, just trying saying it a few times.
How many times?
Some studies have even tested how many times a message should be repeated for maximum effect. These suggest that people have the maximum confidence in an idea after it has been repeated between 3 and 5 times (Brinol et al., 2008). After that, repetition ceases to have the same effect and may even reverse.
Source: The Illusion of Truth