You should remember why you did this, but without the actual memories, there's no context for the decision. So here's the reminder: you did this because you needed to. These memories make it impossible to move forward. You're better off without them. But I wouldn't trust me either. Our memories have just been altered; you'll want to know what you've lost and why you chose to lose it.
The first level of information will tell you the bare minimum. The second level is to keep people from using your lack of knowledge to manipulate you. The third level will get detailed.
LEVEL ONE
There are two people on this ship involved with the four years of memories you had removed. One was your mentor, the other is mostly irrelevant except you "replaced" him as your mentor's assistant. You were never close.
Your mentor trained you as a vigilante from the age of twelve through age sixteen. He's where the majority of your skills come from. You died when you were sixteen, and were resurrected roughly six months later. You spent a year recuperating from the injuries left over from the assault that killed you, after which you decided to continue training apart from your mentor, with whom you had grown to disagree with on key moral issues namely, whether killing criminals (rapists, murderers, drug dealers) was allowable or not. During a confrontation with the criminal that killed you (at this point you were nineteen), your mentor killed you instead.
LEVEL TWO
Mentor: Bruce Wayne
Predecessor: Dick (yes, really) Grayson
Successor: Tim Drake
You were killed by the Joker. Bruce did not kill the Joker. Three years after your death, Drake became the new Robin. You once went after Drake, but he proved himself to be capable enough, even if he wasn't able to beat you. Like Dick, he's irrelevant. Just focus on keeping away from Bruce.
You may be wondering what the fuck brought us back I don't know. Does it matter? Lots of weird shit happens in our world, and I suspect we were just a side-effect. Otherwise, we wouldn't have spent a whole fucking year in a coma or wandering around Gotham with fucking brain damage until Talia picked us up. On the off chance that she shows up, we do owe her a lot. She saved us, she believed we were still alive when everyone else thought we were dead. But she wants to use us against Bruce. She funded everything we did, found us teachers, gave us information, at first to stall us but then to hurt him. Maybe she does feel for us, in her own way? But it's not real, and even if it were, it's nothing compared to the way she feels for Bruce. Don't let her trick you.
Hush (Thomas Elliot) could show up. But he doesn't know shit, even though he'll probably act like he does. You worked with him once to test the waters with Bruce. It's probably not a good idea to do it again. He's obsessed with Bruce, it's honestly a little weird. Okay, fine, lots of people are obsessed with Bruce, but Elliot is just fucking obnoxious about it. He quotes Aristotle a lot. Don't trust him.
The Riddler (Edward Nashton/"Nygma") is aware of who you are and who Bruce is. Don't worry about it. He's smart, but he has nothing over you. Don't let him convince you otherwise.
LEVEL THREE
If you've come this far, you might as well try to get your memories back. Did you really think I was going to write all this shit down for someone else to find?
BRUCE'S NOTE
You're going to let this happen because it'll be better for both of us. You're going to help me "get better" by staying away. Because you still give half a shit. I know you do. You could never let go of anything, even especially if it'd be better for you. But you're going to let go now, because I'm losing those four years so I have a chance to move on. Patrick will have a hell of a time convincing me to stop killing criminals, but at least he'll have a chance now, with those memories gone.
I'm telling you because you deserve to hear it from me and not Patrick.
Maybe you regret those four years. They were the best four years of my life. But I can't stay the person they made me. I can't let go either. This has to stop, so I've stopped it.
I left myself enough information to keep everything straight. I did this for me, but it's a gift for you, too, if you can see it that way. The only thing I have left to give you. A little freedom.
OOC Notes
Jason is a veritable fount of self-misinformation; everything he wrote is questionably accurate at best, so please don't think I'm some crazy Jason apologist. These notes are hidden on the top of his door (they aren't thick enough to affect how it feels when you open or shut the door) and written in code. I am betting that if this plot even happens (Jason is still thinking it over) it will not last two months before he tries to get his memories back, but we'll see. The note to Bruce has not been sent and may never be, but if you would for some reason like to have your character find it, or the other notes, just ask.
[Private to Patrick Kenzie]
Can we talk about the memory thing in person?