The scripture Kalpa Sutra tells about 25 lives of Lord Mahaveer before he attained to the Supreme. In these 25 lives he tried all methods, even being a Dandi Swami, but could not attain the Absolute.
Lord Buddha wandered from one Guru to another and perfected many practices. But none of the Gurus or their teachings could reveal the magnificence of the Supreme. It was when the Light of the Self was revealed to Gautam that he attained Buddhahood.
Nanak taught about Sat (Supreme Truth) being the only Guru. But his followers started worshipping him as the Guru and his own sons indulged in Mantra and Tantra and went wayward!
Do their lives teach us nothing?
In each age there are thousands of Gurus with their own methods and teachings. But none of these - Japa, Tapa, meditation, Tantra or worships can lead to the Supreme. Only the Supreme Truth can lead to the Supreme. Realising it one sees the Holy Light, the Jyoti, the Noor-i-ilahi, say the scriptures. But the so called Gurus go on preaching their own methods - going against the scriptures and even great prophets like Buddha, Mahavir and Nanak.
