Brook's Law
"adding manpower to a late software project makes it later". This law is derived from [#brooks-mythicalmm]. Even though it captures the main idea, the author considers the law a gross oversimplication.
https://en.wikipedia.org/wiki/Brooks%27s_law
[#brooks-mythicalmm]: Brooks, Frederick P. The Mythical Man-Month: Essays on Software Engineering. Anniversary ed. Reading, Mass: Addison-Wesley Pub. Co, 1995.