Sense

As we grow older, more sweet and bitter experiences are etched into our hearts. We learn that trust is a precious gift that should be given to others with care and awareness. Now, unlike before, we trust fewer people because we know that trust is not based on appearance but on the depth of actions and their consistency.
Perhaps the number of people we rely on has decreased, but the value of each one of them means the world to us.

Exactly.
Adulthood is a completely different world; the experiences we go through are no longer just surface wounds — some of them cut deep, all the way to the bone.
Misplaced trust is one of those deep wounds.

Trust is a deep and delicate matter. Each of us, throughout life, may have been hurt in this area multiple times. 
Even the most experienced individuals sometimes have to walk this path again, for understanding hearts is never an easy task.