Yōga Sūtra 4.21

चित्तान्तरदृश्ये बुद्धिबुद्धेरतिप्रसङ्गः स्मृतिसङ्करश्च।

cittāntaradr̥śyē buddhibuddhēratiprasaṅgaḥ smr̥tisaṅkaraśca।

[चित्त अन्तर दृश्ये बुद्धि बुद्धेः अति प्रसङ्गः स्मृति सङ्करः च।
citta = the Chitta; antara = internally; dr̥śyē = when observed; buddhi = intellect; buddhēḥ = used to intellectualize itself; ati prasaṅgaḥ = becomes over thinking; smr̥ti = memories; saṅkaraḥ = getting mixed up; ca = and;]

When the Chitta is observed internally, the intellect is used to intellectualize itself, which becomes overdoing because of mixed up memories.