Tā zhīsuǒyǐ chénggōng, shì yīnwèi tā cóngbù fàngqì.
The reason he succeeded is that he never gave up.
Tips
grammar
之所以...是因为... is a fixed pattern meaning 'the reason ... is because ...'. 之所以 introduces the result, 是因为 introduces the cause. The cause-effect order is reversed compared to 因为...所以...
