Your are in the supermarket, which soda do you buy?
Though the content of the product will be the same, most consumers prefer the soda with the famous logo on the left, just because they have seen this logo many times before. This is the mere exposure effect.
The main application of this bias is in advertising but it also affects other decisions such as cooperating with partners or hiring people we know better. The mere exposure effect is also involved in home bias which triggers you to invest in areas we know better.
Zajonc and al.
Here is the description by Wikipedia of one of his most famous experiment :
Zajonc tested the mere-exposure effect by using meaningless Chinese characters on two groups of individuals. The individuals were then told that these symbols represented adjectives and were asked to rate whether the symbols held positive or negative connotations. The symbols that had been previously seen by the test subjects were consistently rated more positively than those unseen. After this experiment, the group with repeated exposure to certain characters reported being in better moods and felt more positive than those who did not receive repeated exposure.