我让诺言在悬崖上荡秋千
[wŏ ràng nuò yán zài xuán yá shàng dàng qiū qiān]
It metaphorically means that the person is making promises that could be seen as reckless or uncertain, as letting a vow 'swing' suggests an airy, potentially precarious situation, similar to swinging on a cliffside swing.