Consider a Spherical Cow
When making a decision, it’s easy to get bogged down in the details, particularly the quantitative details (a.k.a. numbers).
Instead, this tool encourages you to make an educated guess by doing some “back of the envelope” calculations. Specifically, it encourages you to use rough estimates to see if something seems feasible before committing to the work of getting specific.
The name of this tool (Consider a Spherical Cow) is a representation of how rough your estimates can be: if you need to know how much a cow weighs to make your decision, imagine that the cow is a sphere filled with water. Is a cow actually a sphere? No. And is it actually filled with water? No. But an estimate made this way will be better than no estimate!
In your Project Quartz journal, rough out the numbers that your decision will be based on. If you can quickly find an accurate figure, feel free to use it (FYI, the average weight of a cow is 1,100 lbs), but if you can’t, simply use an educated guess. If the path you’re considering seems feasible based on your quick back of the envelope calculation, then consider putting in the work to get better numbers.
Source
Consider a Spherical Cow: A Course in Environmental Problem Solving (1988) by John Harte