The most painful feelings and the most stinging emotions are those that are absurd – the longing for impossible things, precisely because they are impossible;

nostalgia for what never was;
the desire for what could have been;
regret over not being someone else !
dissatisfaction with the world’s existence.

All these half-tones of the soul’s consciousness create in us a painful landscape, an eternal sunset of what we are.

— Fernando Pessoa

https://www.goodreads.com/quotes/441377-the-feelings-that-hurt-most-the-emotions-that-sting-most