Chapter 11 opens with Arjuna declaring himself well. You have told me the highest secret, he says at 11.1, and this delusion of mine is gone.
He is wrong. A few verses later he asks to see Kṛṣṇa’s universal form, and what he sees undoes him. He loses his bearings. He shakes. He begs for the gentle form back.
The teaching goes on for seven more chapters. Then, at 18.73, Arjuna says it again, with the same word, moha: my delusion is destroyed. My memory has returned, by your grace. I stand free of doubt and will do as you say.
280 verses separate the two cures. The first came from hearing. The second came after he had been shaken and taught again.
He heard it from Kṛṣṇa himself, and still needed it twice. Most of us need it more than that.
The verses
BHAGAVAD GĪTĀ · 11.1अर्जुन उवाच
मदनुग्रहाय परमं गुह्यमध्यात्मसंज्ञितम्।
यत्त्वयोक्तं वचस्तेन मोहोऽयं विगतो मम।।
arjuna uvāca
mad-anugrahāya paramaṁ guhyam adhyātma-sanjñitam
yat tvayoktaṁ vacas tena moho ’yaṁ vigato mama
Arjuna said, "To show favor to me, You have told me that most profound mystery concerning the Self; by that, this delusion of mine has been dispelled."
BHAGAVAD GĪTĀ · 18.73अर्जुन उवाचनष्टो मोहः स्मृतिर्लब्धा त्वत्प्रसादान्मयाच्युत।स्थितोऽस्मि गतसन्देहः करिष्ये वचनं तव।।
arjuna uvāca
naṣṭo mohaḥ smṛtir labdhā tvat-prasādān mayācyuta
sthito ‘smi gata-sandehaḥ kariṣye vacanaṁ tava
Arjuna said, "My delusion has been destroyed, and, by Your grace, O Krsna, I have gained knowledge (Smrti). Freed from doubts, I stand steadfast, and I will fulfill Your will."
Going deeper
Chapter 11 opens right after chapter 10, where Kṛṣṇa tells Arjuna that he holds up the whole universe with a fragment of his power (10.42). In 11.1 Arjuna says that out of favour to him Kṛṣṇa has told the most profound secret about the Self, and that his delusion has been dispelled. 11.2 adds that he has heard in detail how beings arise and dissolve. Chapters later, the claim returns. 18.72 is Kṛṣṇa's last question: has your delusion, born of ignorance, been dispelled? 18.73 is the answer: my delusion is destroyed, and by your grace I have gained understanding; free from doubt I stand firm and will do as you say. The same word, delusion, sits in both statements. Between them lie the vision of the universal form and the rest of the teaching. See chapter 11, chapter 18 and what the Gītā says about doubt.