Just imagine it, meeting somebody who knows you in the future.
You don't believe it at first, of course, but after he's proven it, you slowly realize that the way he looks at you is proof enough. There's this warm familiarity in his bright blue eyes that nobody would bother trying to feign for some elaborate prank. He does know you. Someday, he's going to be your best friend, and you'll know how to look at him like that too.
He's so much younger than you are, even now. You'll be an old man in the future, and this teenaged boy with big dreams and a constant fire beneath him is going to want to spend his time with you anyway.
And just by the way he talks to you as though he's already known you for ages (he has, of course), you find yourself talking to him that way, too. He's the only person in town that takes you seriously at all, let alone genuinely believes that you'll do something so incredible it'll surely land you among your idols, the great inventors of history. Of course this would be your best friend. Both of you need someone to believe in you, and both of you are so good at believing.
The days go by. You know exactly when he's going to leave. You're doing everything to protect him and assist him, risking your own life for your plan without a second thought, knowing that one wrong move could guarantee he'll never exist at all. And even in the best-case scenario, there'll be no way to know whether the two of you will meet again. His presence here alone could have triggered a butterfly effect that would mean your paths never cross at all, and you'll have to wait almost thirty years to find out.
That doesn't matter, though. What's important is that he's going to live.
The plan works. He's gone in a flash of light, leaving your entire world changed for the better as you celebrate alone between the tire tracks he left behind him.
You wait. For decades, you wait. You never forget his name, his clothes, or the way he looked at you. You never stop working on the project that will someday, somehow bring him to your past self again. He tried to warn you that the pursuit of it was going to kill you someday, and you refused to listen. But you kept the pieces of the letter, of course. It was your only souvenir of having met him.
When you finally see him again, you want to hug him and never let go. But he doesn't know you yet. So you act casual, you pretend, you let things happen naturally. You hadn't fully bought that you could end up so close with someone like him, but within a month or two it's as though you had known each other forever. One day he looks up at you in just the way you remember. Those blue eyes were worth the wait.
You swore once that you would never read the letter. You've read it a thousand times since. It all happens just the way he said it would, and sure enough, he's saved your life.
You have so many adventures ahead of you. You'll never lose him, not forever. The two of you have all the time in the world.
