All negativity is irrational since it is not logical to be negative vibrationally speaking. Traditional logic would allow for you to be negative since it is based upon the idea that there is such a thing as an objective truth which is irrefutably true from all perspectives. In reality though, truth itself is relative in that everyone perceives their own form of truth. Thus, what is true is only the vibration you are maintaining since that is what's perceived as your reality.
Ergo, all you ever do with your every thought is set your own personal vibration. When you are being positive, you are setting your vibration to a more desirable frequency, and this is perceived as the more desirable reality that is then experienced through thought. When you are being negative though, you are then experiencing a less desirable reality through thought.
This is precisely why negativity is irrational since in the experiencing of negativity you are only experiencing a less desirable reality, and the greater is the amount of negativity experienced, the more extensively is your reality then decreasing in desirability. This makes your positive thoughts the only rational thoughts you ever consider, because it is irrational to consider thoughts that make your reality less desirable and it is perfectly rational to think thoughts that make your reality more desirable.
The more desirable do your thoughts become, as is indicated by a more desirable emotional state, the greater is the degree to which you are then being rational. It is for this reason that you should always attempt to counter negativity with additional positivity, and perhaps go even further by deliberately seeking out increasingly desirable thoughts, since such thoughts will increase the desirability of your reality to the greatest degree.
Such improvements are immediately perceived in the form of thought too. In the second you begin to think more positively, those positive thoughts are a direct indication of your reality increasing in desirability since such thoughts form a part of your reality. Ergo, in the thinking of a positive thought, you are then experiencing a more desirable reality, and the more desirable is the thought you are thinking, the more desirable is the reality then being experienced.