Imagine, there is a big fire in a house and someone is trying to extinguish it by pouring water from a coffee mug. This person has the right intention (the vector of his deeds points in the right direction -- stopping the fire), but insufficient (the vector length is too short compared to a fire -- too little water).
What do you call a situation like this in English?
In other languages there are following idioms I'm aware of:
- Drops on a hot stone in German (Tropfen auf dem heissen Stein)
- Drop in a sea in Russian (Капля в море)
Note that it's different from fixing a hopelessly broken process in that the process the person in question is doing is generally right (pouring water to kill a fire), but its intensity is insufficient.