It would take time, he supposes, to regain his memories.
But it's hard because he has to plan and plan for the next battle, and the battle after that, and then plan, train, plan. There's little time for reprieve and if they stay at one place for too long, they'll get ambushed and soldiers would get injured and then the nights he's lost over the plan for the following battle has to be scrapped for a new one to account for the soldiers' injuries. And when they get through the battle with no casualties on their side, it's time to march towards the next one.
No time to regain lost memories. There's only time for fighting, more bloodshed, more grueling losses on the other side, more cheering on their side, more ruins of villages to go through, more tears, more fighting, more planning.
Sometimes Robin wonders how it would be like, if he hadn't woken up without his memories. If his mind had been all intact when he woke up on the side of the road to see Chrom and Lissa, who's not delicate, and Frederick the Wary. Would he have led a more stabler life then?
No. Not really. Not if there was that bandit attack on Southtown, not if he still wears his bleeding heart of gold (something the other Shepherds called him), not if he - he stops.
What if he's not who he thinks he is?
Suddenly he has to sit down and think, because what if his bleeding heart of gold is a blatant lie? What if, before he lost his memory, he was someone else entirely? It's something that churns his stomach, that sends his not-all-together mind reeling.
Maybe, he thinks as he stands up, maybe it's better if he doesn't remember at all.
Maybe, he thinks as he straps on his sword and gathers his tome for the next battle, maybe it's better to keep planning, fighting, moving on. Because this war is probably the only way he has to keep himself sane.
More blood. More sacrifices. More tears. More planning, fighting, marching -
No more remembering.