We all know that Franz Liszt were able to amaze his audiences by his stunning technical and musical capabilities.
And we have all heard some stories (sightreading the handwritten script of Griegs a minor etc..).
But what was Liszts weaknesses? Did he have any? Or was he just superhuman like it could sound? 
I have a couple of items to contribute to this. One is from Arthur Friedheim, one of Liszt's more famous students, who wrote a memoir partly about his studies with Liszt, and partly about his career afterwards. Concerning Liszt's technique, he wrote;
"Liszt's technique has been the subject of much discussion and conjecture on the part of those who never heard him. Was it so prodigious, and has it been equalled since? The answer is that it was truly prodigious but that in certain respects it has not only been equalled since, but also surpassed. Moriz Rosenthal and L. Godowsky went beyond Liszt in specialized phases of
mechanisme. However, while Godowsky's chief
metier was dexterity of fingers and Rosenthal concentrated on brilliance and power, Liszt shone in every department of technique and probably never has been approached as a builder of "orchestral" climaxes, overwhelming masses of sound and exciting effects."
Wagner said in a letter to Liszt that he thought L. was the "greatest musician in the world." That being said, when he first met Liszt, Wagner was not a known composer, and was just invited to a piano concert of L's. He went and heard it and in his words, from his autobiography, wrote, "I listened to several of his most brilliant pieces... and went away with nothing more than a feeling of stupefaction." He does not mean it positively, but rather that he found Liszt's performance more overwhelming than profound. Liszt himself regretted some of his earlier performances, especially his way of ornamenting composers such as Chopin, Beethoven and Mozart, and became a different musician in his later years. He was so great as to be able to transform his weaknesses into his strengths.
Walter Ramsey