You practice and practice and practice at earth jutsus.
You've never liked them. You're a specialist at heart, and you've only ever learned the most basic of earth techniques. Your soul is made for lightning, an affinity stronger than any your academy teacher had seen before. You've always loved the biggest, flashiest, most dramatic jutsus best. You didn't have time to mess around with dirt. You're a genius and an arrogant one, you had no reason to try jutsus you weren't good at.
So now you learn earth jutsus as penance.
Lightning was no use in the cave. It didn't matter how powerful or how dazzling your techniques were. They didn't save Obito.
Maybe, if you had known earth techniques you could have done something, and Obito would not have had to take the death that should have been yours. Or maybe, if you had known anything, anything at all, about tunneling or excavation jutsus, you could have somehow rescued him from under the rubble, and Rin could have saved him.
But you never cared about saving your comrades.
So you practice earth jutsus. Even though Obito's eye burns in your skull, a gaping wound in your chakra. Even though you are exhausted in a bone-deep way, in a broken, soul sucking, aching way. Because when your father died you had something to prove, but now you are merely lost and everything you are seems pointless and empty, and the sadness swirls round you and you think you might drown if you look at it too hard.
You keep practicing earth jutsus. Earth feels slow and clumsy and drags heavily at your chakra in a way that lightning never does. You hate it, which is why you don't stop. You don't let so much as a spark crackle over your fingertips, because lightning has always made you happy and you don't deserve to be happy, because you are good at lightning and that's inappropriate because you're not good at being a person.
You keep practicing earth jutsus until there's dirt under your fingernails and dirt clogging your mask and dirt burrowed under your skin, itchy and scratched and miserable, until you pass out half-buried in the training ground.