Whats the reason behind picassos blue period?

Walmart had a sale on blue paint. But seriously, it was a reaction to the suicide of his friend, Carlos Casagemas.

He was very sad probably because time after, when he started cubism, Braque told of him that he drank fuel and spited fire. He was still in Barcelona and Mediterranean sea is definetly blue. He was painting classical motives. Perhaps he thought that painting in blue would be fashionable; after he copied cubism, surrealism or whatever other thing

Im not sure, but if someone has a blue period , there defo some sort of infection ... I think your 'friend' picasso needs to see a doctor :/