This basic principle, governing the Cosmos has been described repeatedly in the various articles published over the past few years on this site. I get a lot of mail and queries from certain advanced practitioners seeking to practice certain Mantras, which have been classified as Tamas Guni, Aaghori or Fearsome and Destructive Mantras, like Maran, Videshan and Uchchatan Mantra, Yantra or Tantras.
Those wishing to practice Tamas Guni Tantras should remember the basic principle and then decide the nature of the Tantra they seek to Master and work within its framework. A great example of relative good and evil would definitely be that of the Rakshaka King Ravana [the personification of evil] who merged into God, because the last word, which he uttered before God, killed his was the name of God.
Does this mean that, anyone can do what he pleases? The answer is no. One of the basic rules, which govern the Three Gunas, is to always maintain the balance between the Gunas. If for example, the Tamas Guni Kriya or action starts nearing absoluteness, the other Two Gunas, the Satva Guna and Rajas Guna start hindering and blocking its progress and the Tamas Kriya is stopped or destroyed. Thus it is left to the freethinking and good senses of the Sadhak to choose his own path and its limits.
The same principles of the Three Gunas work for the common person in his day-to-day life. You can also call it the basic Law of Nature or the Working of the individual accumulated Karma; it catches up with one all when one starts nearing the pre-determined threshold of absolute, good merges into the absolute good and evil into the absolute evil.
Some years earlier, I had written a similar article on the Indian Prophecy and its working and movement through the Satya Yuga to the present day Kali Yuga, you could see that article – Here.