I've been thinking a lot lately about my "one thing." The thing that matters the most to me. Antoine de Saint Exupery gave me language for it: One sees well only with the heart. The essential is invisible to the eyes.
It takes training to be able to "see." (Well, at least for adults. I believe children have a greater capacity for seeing with their hearts.)
For most of us, seeing that which is invisible takes practice.
But it is also possible.