A skilled writer draws material at will when composing.
Tips
history
From Su Shi's poem 《次韵孔毅甫集古人句见赠》 (Song dynasty): "前身子美只君是,信手拈来俱天成" — praising his friend for quoting Du Fu with such ease that every line looked natural.
usage
Highly complimentary. Describes effortless mastery — not luck, but deep accumulated skill. Common for scholars, writers, musicians, and orators.