Because I LOVED this movie and Groot:
[Groot grows a cocoon of branches to cover his friends]
Rocket Raccoon: No, Groot... don't do this, you'll die... why are you doing this?
Groot: WE are Groot.
-from Guardians of the Galaxy
sac·ri·fice noun \ˈsa-krə-ˌfīs, also -fəs or -ˌfīz\
: the act of giving up something that you want to keep especially in order to get or do something else or to help someone
- Merriam Webster Online Dictionary