When you've finally made up your mind about something, do you want it unmade? Of course you don't, and whether you know it or not you make sure that everything in your brain stays the way you left it. This is where "selective exposure" comes in.
Selective exposure is a pretty simple concept. We choose to expose ourselves only to certain facts. We can do so even when contrary facts are staring us in the face.
The first and simplest step in selective exposure is avoiding any information or arguments that potentially contain information that runs contrary to your opinion. Pretty much everyone does that. Whether it's a moratorium on reading about new smartphones after we've just bought what we think is the best smartphone, or routinely turning to the news channel we know is going to look at events from our political standpoint, everyone avoids information occasionally.
The second step is a bit harder. It involves looking at a source that provides us with both information that opposes our viewpoint and information that confirms our viewpoint. The trick is, we have to walk away seeing only the latter. It seems impossible, but it's easily done. All we have to do is decide that the information that opposes our viewpoint is slight and circumstantial, and the information that confirms it is weighty and important. Given time, we can forget the contrary information altogether. (This is both how we remain convinced of our politics and are sure we won every argument we ever had online.)
Sometimes this selective exposure is due to deep, horrible conflicts. We can't bear to think about a loved one's guilt - or our own - and so we turn our face away from anything that might prove it. We dread the consequences of a theory so much we convince ourselves it isn't true. On the other hand, it can take only the slightest push for us to commit to thinking only one way. One study found that people went selective when presented with a piece of information much more often when the person giving that piece of information was "physically attractive." So if you want someone to turn a blind eye, put on your lipstick.