We need to transcend our thoughts and desires to truly understand philosophy and the universe as a whole. However, in our everyday life, we deal with the micro universe and with our own affairs. Therefore we need to use our brain. To practice Tao is not to rid yourself of all thoughts. There are actually more occasions when you would use your true intention instead of non-desire.
The only reason we try to have no thought is to understand the universe, but how often do you want to understand the universe in your everyday life? The majority of the time you are dealing with your everyday life, so be careful not to go to the extreme.
The intersection of the macro universe and the micro universe will create a gate, or a door. Lao Tzu called this "the door to all wonders". This is where yin and yang merge harmoniously. This is also called the Middle Way.
If you cannot observe it, then you must meditate, contemplate and imagine it. It is wondrous that if you contemplate long enough, then eventually you will see it. When you are able to see something that cannot really be seen - that is wondrous.