Lord Nrsimhadeva is the half-man, half-lion form of Krishna who appeared to protect His pure devotee Prahlada Maharaja when his father, the demon Hiranyakasipu, tried to kill him. So devotees of Krishna adore and worship Lord Nrsimhadeva and He protects them in times of difficulty when the demons are attacking. It is the nature of the demons to attack the devotees and the devotees tolerate this. But Lord Nrsimhadeva does not tolerate. He protects His devotees and kills the demons who want to attack them.