How do we know our methods are valid? In academia your customers are primarily other academics, and in business they're whoever has money to pay. However, it's a fallacy to think academics don't have to answer outside of their ivory tower or that businesses need not be concerned with expert opinion. Academics need to pay their mortgages and buy milk, and businesses will find their products or services aren't selling if they're clearly ignoring well established principles. Conversely, businesses don't need to push the boundaries of science for a product to be useful and academics don't need to increase market share to push the boundaries of science. So how do we strike a balance? When do we need to seek these different forms of validation?
Academics Still Need Food
Some of us wish things were so simple, that academics need not worry about money nor businesses about peer review, but everything is not so well delineated. Eventually the most eccentric scientist has to buy food, and every business eventually faces questions about its products/services. Someone has to buy the result of your efforts, the only question is how many are buying and at what price. In academia, without a grant you may just be an adjunct professor. Professors are effectively running mission driven organizations that are non-profit in nature, and their investors are the grant review panels who greatly consider the peer review process in the awarding process.
Bridge the Consumer Gap
Nothing goes exactly as planned. Consumers may buy initially, but there will inevitably be questions and business representatives can not possibly address all those questions. A small "army" may be necessary to handle the questions, and armies need clear direction, so businesses are inevitably reviewed and accepted by its peers. The peer review helps bridge the gap between business and consumer.
Unlike academic peer review, businesses often have privacy requirements for competitive advantage that preclude the open exposure of a particular solution. In these cases, credibility is demonstrated when your solution can provide answers to clients' particular use cases. This is a practical peer review in the jungle of business.
Incestual Peer Review
You can get lost in this peer review process, each person has their thoughts which they write about, affecting others' thoughts which they write about, and so on and so forth. A small group of people can produce mountains of "peer reviewed" papers and convince themselves of whatever they like, much like any crazy person can shut the outside world and become lost in their own thoughts. Godel's incompleteness theorem can be loosely interpreted as, "For any system there will always be statements that are true, but that are unprovable within the system." Godel was dealing specifically with natural numbers, but we inherently understand that you can not always look inward for the answer, you have to engage the outside world.
Snake Oil Salesman
Conversely, without peer review or accountability, cursory acceptance (i.e. consumer purchases) can give a false sense of legitimacy. Some people will give anything a try at least once, and the snake oil salesman is the perfect example. Traveling from town to town, the salesman brings an oil people have never seen before and claims it can remedy all of their worst ailments; However, once people use the snake oil and realize it is no more effective than a sugar pill, the salesman has already moved on to another town. Experience with a business goes a long way in legitimizing the business.
Avoid Mob Rule
These two forms of legitimacy, looking internal versus external, peer review versus purchase, can be extremely powerful, rewarding, and a positive force in society. Have you ever had an idea people didn't immediately accept? Did you look to your friends and colleagues for support before sharing your idea more widely? This is a type of peer review (though not a formal one), and something we use to develop and introduce new ideas.
Conversely, have you ever known something to be true but can't find the words to convince others it is true? In The Matrix, Morpheus tells Neo, "Unfortunately, no one can be told what the Matrix is. You have to see it for yourself." If people can be made to see what you know to be true, to experience the matrix rather than be told about it, they have more grounds to believe and accept your claims. Sometimes in business you have to ignore the nay-sayers, build your vision, and let its adoption speak for itself. Ironically there are those who would presume to teach birds to fly, and businesses may watch the peer review process explain how their vision works only to then be lectured on why they were successful.
In legitimizing our work, business or academic, when do we look to peer review and when do we look to engaging the world? This is a self similar process, where we may gather our own thoughts before speaking, or we may consult our friends and colleagues before publishing, but above all we must be aware of who is consuming our product and review our product accordingly before sharing it.