After certain time period, the brain just gives-up on the hunger for knowledge, giving-up won't be the right word but, inside our soul, mind and brain just accepts that the universe and its anomalies are way bigger than we can ever understand, thus in past many saints and sages just accepted their existence is only for time being (just fraction of entire manifestation) and without any further thought they just got absorbed into the lemniscate. May be our brain is too small to comprehend everything in one lifetime.