I see... the lack of proficiency is simply due to the short time he's had it.
The analogy Yaoyorozu mentioned during combat training was actually correct... no wonder he can't use it well.
But if that's the case, then it's even more impossible for him to master it with just 'image' or 'feeling'... my hatred toward whoever gave that guidance keeps growing.
Image is certainly important. But it can't be just 'image' alone.
As I keep saying, what's important is accumulation.
"Midoriya. I'm going to give you advice assuming you're a complete beginner with the 'Quirk' itself... first, the basic premise. The 'Quirk' is part of your body. Especially for Enhancement-types like us."
Midoriya nods.
"That's precisely why, for Enhancement-types, combat, even when using 'Quirks', still occurs as an extension of our own bodies. Midoriya, from what I felt when touching you yesterday and the day before, you've trained your body quite well and built something respectable. But that alone probably isn't enough."
"I need to train my body more... is that it?"
"No, not that. For example, Midoriya, when you use your special move, how exactly do you do it?"
"Um... in my arms or legs, during the physical test in my fingers... in other words, I concentrate my awareness on the part where I want to exert power, tense up as if gathering power... and release it with the 'SMASH!!' shout, something like that."
"I see. Midoriya, you probably... place too much special importance on your 'Quirk.'"
"? Special importance?"
"Aren't you thinking of your own 'Quirk' as something like a 'special move' that's only released at the moment of attack?"
"Huh...?"
"Like how inputting a command in a game makes a special move come out, or how aiming a gun and pulling the trigger makes a bullet fly out and kill the opponent... you're thinking of it as a momentary, instantaneous 'technique.' I think you're considering your 'Quirk' as that single blow from your fist at the moment you shout 'SMASH!!' That's everything, you think... how about it?"
"...Now that you mention it, that's certainly..."
Bingo.
For Midoriya, All Might's special moves are probably something special as images. Because he's a big fan and knows them well, because he has clear images formed, releasing power as if reproducing them isn't difficult. He can do it smoothly.
(But, that's all he can do... no, I should say that's the only thing he can do, or rather, that's what ends up happening.)
As I thought, this guy... essentially... ended up being able to easily produce the ultimate result while completely ignoring what should be built up along the way. Of course his body can't withstand it.
But, as I said earlier, suppressing an image that's already established is extremely difficult. Because it's easier to imagine the 'breaking' level than the 'not breaking' level. Even when trying to imagine the latter, there's a high possibility the former comes out due to some trivial trigger.
In that case, what we should have him do now...
(...Rather than suppressing what he can already do, it would be faster to build from zero!)
"Midoriya, I've decided on the training approach."
"Really!?"
"Before that, about that 'Quirk = special move' theory we discussed earlier, I'll assert that such a thing is impossible, especially for users of Enhancement-type Quirks like us. For activation types... yeah, like Kaminari or Ashido's Quirks, the moment they use their Quirk, the intended phenomenon occurs... and that's the end. But for us Enhancement-types, since we're using our existing bodies, everything from before use to after use, and even the next action, is all connected."
Even if you only train your fists or arms, you shouldn't be able to deliver All Might-level punches.
The shoulders connected to the arms, the torso connected to the shoulders... the abs and back muscles, the twisting waist, the legs and hips planting firmly on the ground, and the head giving commands to move all of these at the optimal timing.
Only when everything is in place, and everything is trained, does the power of a single strike called a 'punch' emerge.
Actually, when I strengthen my arm strength, I don't just strengthen my arms, but everything connected to them, circulating the necessary energy to reinforce them.
Otherwise, if only the arm strength is too strong, the shoulders might dislocate or the back might get injured. If the foundation isn't solid, you can't fully exert power.
However, Midoriya's 'Quirk' somehow manages to do that. Because of that, all that load returns to the arms and breaks them.
"There are two challenges! First, quickly build a 'foundation' that won't lose to the punch's power! And the other one... suppress the punch's power, and by extension the burden on yourself!"
"Foundation... and suppressing the burden... The second one is the same as before?"
"No, we'll change the approach. Until now, Midoriya has been trying to control it by imagining suppressing the 100% attack, right? So, the opposite... learn to adjust by gradually increasing from 0%."
"Huh!? B, but... I don't know how to do that!?"
"That's why we're doing it. The current situation where you only know how to output 100% is strange in itself. Normally with these things, you start by using the smallest force first, get used to it, and gradually the force you can use increases, right? Midoriya suddenly uses the endpoint first, and if he were making that his 'goal' that would be one thing, but he's making it his 'standard,' so he can't adjust. In that case, it's faster and more certain to explore from zero, and that's the proper order anyway. Midoriya himself is the type to make steady efforts and accumulate, right?"
"...!"
"When learning how to use your body and 'Quirk,' the best method is repetitive practice. Repeat many times and learn with your body. But for Midoriya, 'failure = arm destruction,' so he can't take this approach. We can't have him break multiple times every day, have me give him energy, and have Recovery Girl heal him."