Example
nǐ你hěn很róng yì容易bǎ把mǔ yǔ母语shuō说děi得tōng shùn通顺líu chàng流畅，què却hěn很róng yì容易bǎ把fēi非mǔ yǔ母语shuō说děi得bù不zì rán自然。
你很容易把母语说得通顺流畅，却很容易把非母语说得不自然。
It's very easy to sound natural in your own native language, and very easy to sound unnatural in your non-native language.