A few months ago I took an initial position on Diageo. My purchase price was around £31 per share and I made bought enough to make it 4% of my total portfolio. 

Today the company put out a press release announcing that their expected earnings for this coming year are going to be a bit lower than expected. This results in the stock price plummeting 15% today. 

These are the moments I prepare for and as long as my original buy reason is still valid then an investor should welcome these lower prices as opportunities to add to the existing position or just sit tight and enjoy the ride

For now I plan to just sit and watch. If the stock drops a little more and gets close to £25 a share I will likely add to my position, but for now I'm just going to chill and watch the show.