Tā wèicháng shībài guò, suǒyǐ bù zhīdào cuòzhé de zīwèi.
He has never experienced failure, so he doesn't know the taste of setback.
Tips
grammar
未尝不 is a double negative construction meaning 'it is not without' or 'it is not impossible.' 未尝不可 (wèicháng bùkě) = 'it's not a bad idea' is a very common set phrase.