Sharingan Lore

4. Obliviousness of Awakening

There are a few occasions when an Uchiha awakened their Sharingan or gained a new tomoe without even realizing it, so unlocking a Sharingan or gaining a new tomoe may not be a change that is immediately noticeable to its user.

Sasuke and Sarada (and possibly Madara) didn't even notice when they activated their Sharingan itself for the first time. My theory is that Phase I Sharingan is so weak compared to Phase II and Phase III that it's not actually that useful overall and doesn't improve a user's vision all that much. Its effect is so limited that Sasuke and Sarada didn't register any change in their vision at all.

Initially Sasuke didn't seem to realize he had awakened his Sharingan, which is partly why he forget about those hazy memories and assumed he awakened it at age 12. But once his old memories started to resurface in Shippuden, he could look back upon his memories from the night of the massacre and perhaps his experience with the feel of the Sharingan in his teenage years made him realize that the changes in his vision he felt as a little kid then were caused by him activating the Sharingan, even though at age 7 he'd been too inexperienced with what the Sharingan felt like to realize he had awakened it. And since 7-year-old Sasuke seemed oblivious to the Sharingan awakening in his eyes, that also means that Phase I's effect is so limited that it doesn't noticeably change the user's normal vision.

The same thing happened with Sarada, whose emotional distress would turn on her Sharingan without her noticing any change in her eyes. It wasn't until other people pointed out the change in her eyes that she realized she had the Sharingan, and in fact, Sarada didn't learn she had the Sharingan until Naruto provided Sarada with a mirror to show Sarada that she has awakened a Phase I Sharingan.

This leads me to believe that the one-tomoe Sharingan is extremely weak, to the point where during the intense and emotional situations that awaken or activate a Sharingan, an Uchiha can be too preoccupied to even notice when they've awakened the dojutsu.

In the Final Valley fight, Sasuke recognized the marked improvement that his third tomoe gave him and was aware of its effects, but he mistakenly attributed his Sharingan's upgrade power-up to his curse mark instead of recognizing that his sudden power-up actually came from his Sharingan gaining a new tomoe, and who knows how long it took for him to realize that he had at some point gained a third tomoe.

The Mangekyou Sharingan and the Rinnegan seem perhaps like their awakenings are usually most noticeable and users are more likely to be cognizant of the change to those high levels, but that could be partly because they are typically awakened by more perceptive and higher-level users who are more attuned to their dojutsu. Or the Mangekyou and Rinnegan have a drastic change in vision. Or the change is actually just easier to feel and physically more noticeable in some way, such as their vision's improvement being far more obvious than, say, a Phase I Sharingan.

After all, an Uchiha cannot see their own eyes, so unless they are particularly aware of and attuned to the change in their eyes and knowledgeable enough to correctly attribute it to their Sharingan having gained another tomoe, they aren't necessarily going to be aware of the change. Meaning an Uchiha could potentially go for a while without realizing they've gained another tomoe unless they catch sight of their reflection or someone brings that upgrade to their attention.

In the novels Itachi described the Sharingan as adding a red tint to one's vision, but that is evidently not true in every case, since in some awakenings and activations, the users don't notice a change in vision at all.

Likely awakening a new tomoe can be perceived by a perceptive, attuned, informed, and calm user. However, emotionally charged or distracted users may be oblivious to the unlocking of an additional tomoe or even to the fact that their Sharingan has subconsciously activated in response to their intense emotional state.

Phase III Sharingan is evidently noticeable in the great improvements it grants its user since as we saw, Sasuke observed a marked improvement in his skill that Phase III Sharingan gave him, making it noticeably superior to a Phase II Sharingan. But Sasuke was perhaps too far removed from the teachings and knowledge of his clan's abilities (due to his clan's culture being eradicated in the Uchiha massacre) to be fully educated on what changes occur for each stage of the Sharingan, so he mistakenly identified his change in vision as an effect of the curse mark. Of course, it could just be he wasn't thinking about it, since it's not known if being familiar with the clan's lore and knowledge of the Sharingan helps a user recognize when they've awakened it, though I personally think it would.