Whether it is an impulse purchase like a candy bar or a package of cigarettes or an infrequent and highly deliberated purchase like a washing machine a refrigerator, a vacuum cleaner or a mattress, the biggest single thing that advertising can contribute is a friendly predisposition toward the brand—a whole complex of thoughts and emotions which give the purchaser peace of mind in the choice he makes.
We shun the unknown. We are naturally drawn to the familiar.
You might call this simply “friendship for the product”.
Your best friends are people whose qualities you like and admire and whom you enjoy being with— but they are usually people you see frequently.
The principle of frequency in advertising has long been recognized. Several great brands have been built around rigid adherence to this principle rather than through the content or power of any single advertisement.
Excerpt from: Leo: A Tribute to Leo Burnett, Through a Selection of the Inspiring Words that He Wrote or Spoke by Leo Burnett