Pranali means, “the means to achieve,” and siddha means “perfection”. Sometimes people think that this siddha-pranali can be achieved simply by receiving some mantra and one can immediately achieve one’s siddhasvarupa—his eternal relationship with the Lord. However, in this verse of Siksastaka, Srila Bhaktisiddhanta says, “trnad api sunicena.. is our siddha-pranali, because it is not just simply the receiving of the mantra, but it is a character, or the qualities of the individual, in order to actually achieve perfection. In other words, one cannot think that he has achieved siddha if he is devoid of humility. If he is incapable of giving respect to others, he is not tolerant; he is full of false pride and prestige. All these characteristics are the complete antitheses of perfection. The reason why this is the siddha-pranali, is because one has to display all of these qualities, if one wants to achieve the real perfection.
MKV, Vol 2- Pg 44, Five Obstacles of Nistha-Bhakti (Lecture: Kiev, Ukraine—29/4/01)