Getting up in front of a crowd can be an absolutely terrifying experience for a lot of people. It's interesting to note that several studies have found that Americans rank public speaking as their biggest fear, ahead of death (which came in fifth).
Alice Fredenham was scared out of her mind getting up in front of the judges on Britain's Got Talent, because a rejection from them was, in her mind, an indication that she wasn't good enough as a person in general. After she's done singing, Simon Cowell tells her something that leaves her in total disbelief. Just watch and see what he says.
H/T: Britain's Got Talent