Though I'd start another list and see what gems appear from everyone ( even pc branding!) We are all of different levels of experience and knowledge in the design field. But what ONE thing has changed your thinking and made you either better, more enlightened, more driven, stimulated or just threw a complete spanner in the works and made you re-evaluate everything, rightly or wrongly. Suppose I should confess first... Getting fired ( actually got fired twice.. ) But that first time made me realise that I couldn't take anything for granted in this business and I'm only as good as my last piece of work. ( that 'last piece of work' many years ago was suitably shit - hence the P45).