What separates us from the other animals is not our intellect, nor our use of tools. It is our perceived sentimentality; the ability to superimpose an entire world of value on top of practical use. 

It is the reason why we value diamonds more than water: the diamond water paradox.

It is the reason why we stress over an abstract lifestyle: we stress over exams, taxes,  careers and the overall rat race we forged society within when all we need for survival is food, water and shelter.

It is the reason why we celebrate achievements: our first _, our last _, our favourite _. etc.