Why is the quote, "She realized that you can't be weak when it comes to killing; you have to be strong or it just causes more sorrow." important?

Tita's killing of the quail was long standing, she didn't use enough force and the quail went running around the kitchen with a hanging head. Mama Elena was mercilous..... she killed the quail with one blow.

With a deep breath, she took hold of the first one and twisted its neck, as she had seen Nancha do so often, but she used too little force to kill the poor quail, which went running pitifully around the kitchen, its head hanging to one side. She was horrified! She realized that you can't be weak when it comes to killing: you have to be strong or it just causes more sorrow. It occurred to her that she could use her mother's strength right now.

Mama Elena was merciless, killing with a single blow.