Nefesh HaChayim, An Introduction by the Author's Son

And anyone who didn’t witness how my honored father-the-genius (OBM) behaved wouldn’t believe it when told about it. All of his strategies and plotting that he set in place for himself—he made it a habit that all of the novel interpretations of Torah that he developed, whether in G’mara, RaSh”Y’s commentary and Tosafote, or in Responsa, he evaluated whether he was becoming happy as a result of the intellectual effort. He was concerned about gaining pleasure from the words of Torah, and he would carefully examine if his novel interpretation perhaps wasn’t a genuine expression of Torah. [We learn from] the statements of the sages (OBM, start of the perek eiloo d’varim) that anyone who becomes egotistical loses his wisdom (and as a kind of joke he would say that he considered it as a kind of bribe, that he bribes himself with the joy of success). And he would make the effort to disprove his own words and to change his words, and to weigh on the balance scales of his intellect how to genuinely establish a correct theory, and the correct reasoning. And anyone who observed would see and understand in his wisdom that he accomplished it. How he would denigrate his opinion of his own knowledge. His opinion of what he knew would be lowly to him, as the sages stated (Taanit 7a): “Words of Torah only survive in someone whose opinion of his own knowledge is lowly”.