What is 'It'?

This is a focus on low mood associated with bereavement. Sam feels low and fed up, but doesn't understand why he feels this way. Everyone else has an opinion on the change in his behaviour. His teacher thinks he is being lazy and can't be bothered to finish his work, his mum thinks he is moody and bad tempered, his friends think he is no fun any more and turning into a bore. Comments like, 'Cheer up it might never happen', ' What has got into you?' and 'Do you want to talk about it?' just u...