道高一尺，魔高一丈
(Dào gāo yī chǐ, Mó gāo yī zhàng)
"Virtue is one foot tall, evil is ten feet high"

This is originally a Buddhist teaching which means that for every foot (尺) of good or virtuousness (道), there are ten feet (丈) of temptation (魔) waiting to take those on the Path, off it.