Three beautiful words. When used together, one of the most wonderful — if not most underused — phrases in our lexicon. Am I being hyperbolic?
Modern culture dictates that we claim to know, so we spend a lot of time knowing stuff. We expend much effort displaying our expertise.  If we personally don’t know something, we rely on designated “experts,” who tell us they know (despite their unimpressive track record). We know where the stock market is headed. We know how countries will respond to “liberation.” We understand the ins and outs of other cultures. In relationships, we do not hesitate to state unequivocally the others’ thoughts, intentions and motivations. At some point in the past, we have “known” the world is flat, the sun revolves around the Earth and that spontaneous generation exists. Collectively, we know both that “God Exists” and that it doesn’t. We know that the people in our tribe are more intelligent, moral, and civilized than in theirs. Of course, they say the same thing.
Everyday, millions go to work knowing what their customers need and know how to market and sell to them.  Getting feedback on business plans from a “panel of experts” is often an exercise of pure bloviatng.  Executive teams sit at conference tables playing “pass the conjecture.”
Einstein wrote about a lack of knowledge being the key to learning.
Approaching problems with a clean slate, allows one to view problems more objectively, to see things one might not see if filtered through the lens of what you know. His thought experiments were constructed from the perspective of an unknowing observer.
I don’t know.
It’s a powerful idea. It’s liberating.
First, it’s anti-delusional.  To admit that you don’t know (or to accept the premise that you don’t know) is honest.  Being honest with yourself is frees you to explore all sides to a problem.  Being honest with others from the outset instills credibility, even when that honesty means admitting a lack of knowledge.  Try one of these the next time someone asks for your opinion:

I don’t know, but perhaps…
I don’t know, but to find out we could…
I don’t know, but I bet your existing customers do…

Second, while no one is able to completely eliminate personal and cultural biases from thinking, increased self-awareness allows you to potentially minimize or at least account for them.  Denying them may shield  you from a more inciteful answer or more relevant result.
Third, “I don’t know” exposes what you need to test and learn.  If you know social media marketing is the best way to market to your target segment, say, low-tech, late-majority, senior citizens — hey, more power to you!
Open your mind to all possibilities and then use your experience to test.  Hunches are great, but accept being wrong and have a test B (and C, D, etc.) in place.