Huíshǒu wǎngshì, tā hòuhuǐ zìjǐ lùlù-wúwéi de nàxiē nián.
Looking back, he regretted those years when he'd drifted along achieving nothing.
Tips
history
碌碌 is an ancient Chinese descriptor for mediocrity - 《史记·酷吏列传》 already uses '九卿碌碌奉其官' ('the nine ministers just went through the motions of their office'). The four-character form 碌碌无为 cements that sense of 'much busyness, no achievement.'
memory
碌 is the sound of a stone roller grinding away - lots of motion, nothing really produced. 碌碌 = the eternal rumble of effort without result.