To obtain something, something of equal value must be given.

Fool! Nothing but black ink runs through my veins!

Roy: "Looks like it's starting to rain" Riza: "But..It's not raining..." Roy: "Yes it is. This is the rain.

Friends are connected by their souls, you can't just rinse something out that has been deeply instilled into your sou

And now, I'm thinking again, isn't there something we can do about something we can't do anything about?

Hughes: (Talking for Mustang) 'I won't allow you to die under my jurisdiction because it'd be a pain to clean up the mess.' That's what he said. Edward: Fine. Tell him, 'Understood. I'll never die before you, colonel, you @#'$ idiot.' Hughes: Ha ha ha! They say the ruder you are, the luckier you are! In that case, you and Roy are gonna live forever!

So that the new generation that will be born can enjoy happiness. To pay the cost we will have to shoulder corpses and cross a river of blood (Riza Hawkeye -- Fullmetal Alchemist)