Thanos: Little one, it's a simple calculus. This universe is finite, its resources finite. If life is left unchecked, life will cease to exist. It needs correction.
Gamora: You don't know that!
Thanos: I'm the only one who knows that. At least, I'm the only one with the will to act on it. For a time, you had that same will. As you fought by my side, daughter.
Gamora: I'm not your daughter. Everything I hate about myself, you taught me.
Thanos: And in doing so, made you the fiercest woman in the Galaxy.
Gamora: You don't know that!
Thanos: I'm the only one who knows that. At least, I'm the only one with the will to act on it. For a time, you had that same will. As you fought by my side, daughter.
Gamora: I'm not your daughter. Everything I hate about myself, you taught me.
Thanos: And in doing so, made you the fiercest woman in the Galaxy.
Thanos: Little one, it's a simple calculus. This universe is finite, its resources finite. If life is left unchecked, life will cease to exist. It needs correction.
Gamora: You don't know that!
Thanos: I'm the only one who knows that. At least, I'm the only one with the will to act on it. For a time, you had that same will. As you fought by my side, daughter.
Gamora: I'm not your daughter. Everything I hate about myself, you taught me.
Thanos: And in doing so, made you the fiercest woman in the Galaxy.
http://www.moviequotedb.com/movies/avengers-infinity-war/quote_82509.html