“How does a strong player come to lose in just 18 moves? I should know, because I have lost several games just as quickly. If you want to lose a miniature, then here are three helpful tips. First of all, it is a big help if you are Black. Losing in under 20 moves with White requires a special talent which few possess. Secondly, choose an opening in which you try to realise strategic ambitions, but at the cost of backward development and delayed castling. Thirdly, if something goes slightly wrong, don’t reconcile yourself to defending a bad position - seek a tactical solution instead! Don’t worry about the fact that tactics are bound to favour the better developed side; just go ahead anyway. Follow this advice and at least you will get home early.”
I experienced a swift (21 moves) defeat last week, and thought it might be instructive for others to see some good examples of what Nunn says above, from my own games in the last few years - pretty much games where I've been lost right after the opening.
#1: The game from last week, where Andrew broke his losing streak of 4 in our encounters. My rating: 2362, Opponent's rating: 2296