It was never about the shirt - story

This happened in one kingdom far, far from here. The kingdom was ruled by a king who had one daughter. One year his daugher got sick, the king called the best doctors she could find, but none of them managed to help her out. In the end he called the wise men, and when they looked at the princess, they said to him:

• There's only one cure for her illness. She must wear a happy man's shirt for three days, it will cure her. Bring us that shirt.

All enthusiastic and thrilled that they finally find a way to save his daughter, the king summoned four of his best servants and sent them to four sides of the world to search around the kingdom and find a happy man, and bring his shirt.

After a while the first servant returned but without a shirt:
"I went to the end of your kingdom and did not succeed in finding any lucky man."

After that, the second and third servant returned empty-handed as the lucky man was not found anywhere.

Lastly the fourth servant came back, and when the king asked him whether he had succeeded, the servant answered him,
"I asked everywhere and slept at every home looking for someone who was lucky, but without success. And I was already tired and ready to go back when in a village at the end of the reign, I was told that there is a man who lives next to the river and who is happy. Indeed, when I got down to the river I found it finally, the happy man, free like a bird and open hearted

"And?" the king asked with voice full of hope, "did you bring his shirt?"

"But your majesty," servant replied , "he is poor and did not have any shirt.

Unknown author
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Photo from: https://pixabay.com

What is the lesson of this story in your opinion?