The concept that we only use 10% of our brain is based on a quote by William James (1908): "We are making use of only a small part of our possible mental and physical resources."
We actually physically use all of our brain every day, but this does not mean that we use it well or efficiently.
The fact is that we usually know the answer to everything we need or want to know. We just need to be quiet enough inside to hear that inner wisdom that will solve our problems and answer our questions.
Today write down 3 questions you have about your life. Then sit quietly. Use some form of divination like Tarot cards, Ouija board, Palm Reading, etc. It doesn't matter if you don't know how to do use these tools.
Pay attention. Look closely. Listen to what comes up in your mind. Do not judge or doubt. Write.