Mind is frail. Memory of waves of thoughts wavering. Possible repetitions are unintended but forgivable. Leonardo had written about this problem in his Notebook (Vol. I) :
Oh reader! Do not
blame me, for the subjects are many and memory cannot retain them [all] and say: ‘I will not write this because I wrote it before.’ And if I wished to avoid falling into this fault, it would be necessary in every case when I wanted to copy [a passage] that, not to repeat myself, I should read over all that had gone before; and all the more since the intervals are long between one time of writing and the next.