Why are Spain so bad at football?

Spain drew 1-1 with Serbia last night, putting their chances of playing in the next world cup in serious jeopardy. They have the best domestic league in the world, but when it comes to international games, they are rubbish.

I’ve even heard this blamed on the old inter-regional problems polemic – the Basques don’t like the Madrileños, who don’t like the Catalans etc., meaning that it is impossible for them to play well together – but that sounds a little far-fetched…