We have all heard the cliché that two heads are better than one.  Well, there is psychological reason for this beyond simply doubling your potential ideas and intelligence about a particular matter, it is that we tend to see the world through the lens of our training, education and conditioning and attempt to fit what we see in the world to the values and beliefs that we already have.  For example, when all you have is a hammer for tools in your tool kit, you see everything as a nail!  This psychological concept is called confirmation bias - the act of trying to fit what you are currently experiencing into your consciousness but in so doing making sure it aligns with what you already know to be true and believe.  We really see the world as we are, not as it actually is.  This is why when you leverage the diversity of other people, people who have different ideas, thoughts, beliefs and training than you do, you get different ideas about what is being experienced and different solutions to the problems being faced.

We have a habit of distroting the facts until they become bearable for our own views.  Charlie Munger

The confirmation bias leads us to hunt for nformation that flatters our existing beliefs.  Chip Heath & Dan Heath

The question is not what you look at, but what you see.  Henry David Thoreau

What we see depends mainly on what we look for.  John Lubbock