Put a quart into a pint pot
Definition 1 of 1
Pro Tip 1/3Physical Impossibility
The phrase implies a task is as impossible as fitting too much liquid into a small container. 
Expecting one person to do the work of four is like trying to put a quart into a pint pot.
Pro Tip 2/3Cultural Origin
It's a British phrase, so it may not be understood in countries using different liquid measurements. 
He described his new job at the United Nations as trying to put a quart into a pint pot.
Pro Tip 3/3Metaphorical Use
Often used metaphorically for tasks with inadequate resources or space. 
The new software has so many features, it feels like they've tried to put a quart into a pint pot.