If one is pridefull, their arrogance will lead them astray from wisdom. Arrogance and narcisism hold a person back from attaining enlightenment by twisting perception.
If one is pridefull for having beauty and youth, their appearance will block his perception.
If one is pridefull for having much money, the money will block his perception.
If one is pridefull of having fine possessions, the possessions will block his perception.
With something blocking one's perception, one cannot see truth in things, and they will fall astray from gaining wisdom. One who tosses away the attachment to status, money, possessions, and other blinding lusts, can see freely all that is and their mind is not blocked and tainted by distractions. In this way, one can attain buddhahood.
Being pridefull is a poison of the mind, but being proud is different. It is good to be proud of acheivments for they will motivate further imrpovement. It is good to be proud of who you are, your family, and your life. This is more of an intangible pride, and on a lesser scale than being pridefull. In this way; it is good and can drive us to improve. Being proud of having possessions, money, or beauty, will motivate greed and thus blur your mind from wisdom and truth. Being proud of having a caring family, an intelligence, good achievments, and happiness will motivate positive improvement.