山盟海誓不过一句话
[shān méng hăi shì bù guò yī jù huà]
Literal meaning: 'Vows made by mountains and seas are but a single word'. This signifies that grand oaths (historically said to be reinforced by natural entities like mountains and seas for their permanence) are ultimately just words or promises. It has shades of skepticism towards the permanency of big pledges.