Basically we everytime come to know that in order to make a mantra / sadhana work for you, it should be siddha first. There are different types of sadhana / siddhi for different purposes. I wanted to know what happens during a mantra siddhi process. For Ex : If one is doing a sadhana for say 40 days to attain siddhi over some deity for a boon or power. So what obstacles one has to face during and after completion of it.
Update : Also, in Bhagavad Gita as Krishna says that those who worship demigods go to their kingdom, so is it like attaining siddhis is kind of less achievement than attaining moksha/nirvana/enlightenment ?