Full Idea
We can confidently determine the chemical composition of gold from just a single sample, but we cannot determine the height of trees from just a single tree.
Gist of Idea
One sample of gold is enough, but one tree doesn't give the height of trees
Source
Susan A. Gelman (The Essential Child [2003], 06 'The role')
Book Reference
Gelman,Susan A.: 'The Essential Child' [OUP 2005], p.143
A Reaction
The tricky word here is 'confidently'. If you meet one Latvian who is nice, do you assume they are all nice? At what point do you decide gold etc. really are natural kinds, where one sample tells all? Evolution of species...