Our advancement is not because of our endeavor but Krishna's mercy, which is withdrawn when He sees pride within us.
When due to false pride, you disrespect exalted Vaishnavas, You become attracted to bad association. That bad association corrupts and destroys your devotion.
When you are Proud, instead of becoming Grateful , you become Envious.
Inability to find faults in ourselves is a sign of pride and it is a wall between god and us.
Unless one knows about the distinction between life and matter, one will be very proud.
To be proud means to be unrealistic, dishonest and ungrateful.