Many years ago I heard a story in a priest's sermon which has affected me ever since:
A young man wanted to learn how to live in the wilderness, so he found a native american who had grown up in the traditional way for his people, and apprenticed himself to the man.
After many months of long training, it became time for the young man to test his skills. His master gave him the task of killing a dear. He prepared for several days. He got his equipment ready, he observed the dear to know their movements, and he starved himself so that he would need the deer and really, truly want it.
When the day came, he hid in a tree along a path that the deer often followed, his knife in his hand held ready. Several hours went by, and when a buck walked underneath him in the right place, he dropped down onto the dear's back. With his free arm grabbing it around the neck, he stabbed the dear in the heart with his knife until it stopped moving.
When the dear was dead the young man stood their quietly looking at the dear and the blood on his hands. His master walked out of the hiding place from which he was watching. With tears in his eyes he looked up at his teacher and said, "I hate you for making me do this."
The old man held his gaze and replied, "When you feel this way about plucking a blade of grass, then you will be truly alive."
(btw, I believe that there is a version of this story here. Perhaps it is the original)