For good or for ill
There was a silence. At last Elrond spoke again.
‘This is grieving news concerning Saruman,’ he said; ‘for we trusted him and he is deep in all our counsels. It is perilous to study too deeply the arts of the Enemy, for good or for ill. (…)’
– J.R.R Tolkien. Lord of the Rings. The fellowship of the Ring, Book two, chapter II, p. 258. 2001. Harper Collins Publishers.