Jai Sri Ganesha,
No one knows the exact cause and truth unto manifestation of supreme truth in the form of Godhead personality,
Yet time has proclaimed the truth through the saints and sages of ages and the era,
Lord Shiva incarnated as a mystic fire to quench the fire of ego among Brahman and Vishnu, which subdue their self and invoke them to look at the beginning and the end, but both fail to reach at, but Vishnu adore the truth and Brahman take shelter in falsehood to safe guard his might,
And to pacify the subject Lord Shiva manifest in person to reward the truth and penalize the falsehood, Vishnu was rewarded with truth to serve the cause on the planet with time and again, Brahma was limited to the light of wisdom alone through the gracious nature of Shiva, and the day was recognized as Shivratri, a night may help spirit to bloom more than the light of the day,
May Lord bless all,
Thanks please