Rintarou Okabe: Time-leap machines and time machines should never be built! Even if you can figure out how to do it, you should never ever build one!

Kurisu Makise: If I don't do something, you'll vanish. You will never have existed... I have no choice but to change the past!

Rintarou Okabe: And what if you fail? What if it doesn't go well? The answer is simple. You do it again. You keep going back to the past until you succeed. As long as they have the means to go back in time, that's what people will do.

Rintarou Okabe: But it'll only increase the suffering. A change in the past will always affect something else. It will never change in a way that's convenient for you. If you save someone, you will lose someone... Dreams you finally fulfilled won't exist anymore. Your long-held desires will be snatched away, eradicated... and when the change you hoped for doesn't happen, you will have to keep facing that inescapable reality again and again, again and again!

Rintarou Okabe: Do you realize the pain of continuously repeating all of that while bearing the responsibility for all of those losses? Do you understand the fear of losing your humanity after it wears you down?

Kurisu Makise: But...

Rintarou Okabe: Even if you have the means, the past ust not be changed. You must not turn chance into reality.

Rintarou Okabe: No one knows the future. It's because the past cannot be undone that people can accept all sorts of pain, adversity, and cruel accidnets, yet still move forward.

Kurisu Makise: The what are you going to do, Okabe? You're going to disappear! I... I saw it... A world where you don't exist. A lab with only Mayuri, Hashida, and me... Where nobody remembers you... It was crueler than death! Any mark or meaning of your existence will disappear!

Rintarou Okabe: ...I don't care.