[Advaita-l] Why realization is difficult?

[Bhaskar YR]

praNAms
Hare Krishna

What are the obstacles? 

> ajnAna

Who has that? 

>  the person who has this question in his mind & asking it for the 
clarification (reference vide sUtra bhAshya of shankara)

Why is he not able to remvoe them?

>  lack of sAdhana

Hari Hari Hari Bol!!!
bhaskar

PS:  Sorry to be blunt in my reply.  You can expect more elaborated answer 
from Sri Sadananda prabhuji.