Pyaar mein andha ho jata hai, jab Shukra lagan ka manda ho jata hai.
He becomes blind in love, when Venus in the Ascendant becomes bad/afflicted.
The 1st house (Lagan) represents the mind, the head, and the self. Venus (Shukra) is the planet of love, romance, and attraction.
When Venus sits in the 1st house, the person is naturally beautiful and romantic. But Dr. Sharma warns about what happens when this Venus becomes negative or afflicted ("manda ho jata hai").
The romantic energy completely overtakes their brain. They literally become "blind in love" ("pyaar mein andha"). They will ignore all red flags, abandon their logic, and ruin their own life, career, and reputation for a toxic or unworthy partner. They must learn to love with their brain, not just their heart.