A person did 4 years BSc Engg followed by 2 years MS but couldn't get a profession he/she is passionate about. So, is it normal to go for another 4 years BSc Engg degree after which achieving his/her passion is sure?
No, it's not normal, but if you are absolutely sure that another four years spent in pursuing a different degree will make you happier in the long run, and if you're lucky enough to have the financial means to do so, then go ahead. Keep in mind however, that "passion" for a career is often overrated - every job, even jobs that seem appealing on the surface, in reality, is not always exciting, and jobs that don't initially feel like a good fit might turn out to be very rewarding once you gain more expertise and knowledge. Also consider carefully whether you can find a job that is a better fit for you without having to go back to school - plenty of people end up in careers that have nothing to do with their college degree.