Put Out a Burning Wood Cart With a Cup of Water in Chinese / Japanese...

杯水車薪 is a warning against a futile effort.

This proverb literally refers to one who is “trying to put out a burning cart of wood with a cup of water,” or “throw a cup of water on a cartload of wood.” The lesson to be learned is about using the right measure or tool for the job and not wasting your effort if you are inadequately equipped for the task at hand - in other words the postscript should be “go get a bucket or a fire hose.”