It is explained as the knowledge the four Noble Truths also. Right understanding of the first Noble Truth leads to the eradication of the second Noble Truth which is the origin of the first Noble Truth. One who searches for supramundane happiness and final liberation must understand that the first Noble Truth is to be penetrated, the Second Noble Truth to be eradicated, the Third Noble Truth is to be realized and the Fourth Noble Truth is to be followed. This is the brief meaning of Right Understanding. The key-note of Buddhism is this Right Understanding.
Clear vision leads to clear thinking.
The second factor of the Noble Eightfold Path, therefore, is Right Thinking . This important mental state eliminates wrong ideas or emotions and helps the other moral adjuncts to be directed towards Nibbana. Nekkhamma Sankappa - The Thought of Renunciation of worldly pleasures or the thought of selflessness. This is opposed to attachment, selfishness, and self-possessiveness. The thought of harmlessness or compassion, which is opposed to cruelty and callousness.