No book will tell you this because its a little known fact but I'm going to let you in on a secret - the Scottish sports fan is not so distantly related to the wildebeest of the Serengeti.
Specifically the stupid one that doesn't run with the herd. That one you always see on the wildlife documentary, the one that doesn't even know its a wildebeest because nobody has shown it a mirror. It thinks it just hanging out with its wildebeest friends for the day, its seems to think 'I'm not a wildebeest I'm one of those big buggers over there, with the tusks and the trunk, pfft, 4 lionesses don't scare me, I'll stay right here.'
Most of the time the stupidest of the wildebeest die off, survival of the fittest and all that. But enough of them have survived through the generations to spawn the Scottish sports fan. The fan that believes, when everything should be telling him otherwise, that this is the year that Scotland is going to qualify for the football World Cup (nope fucked again), that this is the year that Scotland is going to win the rugby Six Nations (nope fucked again), that this is the game that Glasgow Celtic is going to score one goal more than the opposition (nope fucked again).
The Scottish sports fan is just like the stupid wildebeest that we see in the nature programs, unfortunately they carry on breeding at a faster rate than wildebeest because there is a shortage of cannibals or predators out there that find the Scottish sports fan easy to digest. And so with the link between the survival of the fittest and the evolution of the homo sapien being broken the Scottish sports fan goes on believing in fairy tales.