No Imagination

A bad day today, not simply because I was trading badly, but because I showed no imagination, no adjustment to market conditions when it was called for.
Over the last week or so, someone has been punting huge amounts, 20 to 30 thousand pounds often, on a single runner, and moving the odds by 10 or more ticks. I knew this was happening, but just carried on trading in my normal manner, which usually entails laying first, although its not set in stone, I am just used to looking for opportunities for a drift.
I have managed to avoid him over the last couple of days, but it was inevitable that I would get caught eventually, and so it happened today, for a £15 loss. The loss threw me, and I lost my discipline and control in trying to find ways to exploit the punter. I tried laying another runner when the large amount came in, but instead of going out this runner also came in, for another £7 loss.
I need to use my brain more in thinking about the situation, rather than just carrying on happily as if the market is the same. Maybe these events will help me to identify opportunities other than my lay-first technique.