The topic of this paper, underestimating risk leading to the collapse of the market leader in tourism, is demonstrated on the example of the British travel agency Thomas Cook, which at one time was one of the oldest and largest travel agencies in the world. The aim of this paper is to analyze the development of the stock prices of Thomas Cook from May 13, 2018 to May 19, 2019 and the factors that had an impact on the share price of this company in the monitored period. The base source of data are the share prices of the travel agency Thomas Cook in the specified period from May 13, 2018 to May 19, 2019 published by MarketWatch. A statistical description of time series is used, a moving average trend line is displayed, and a cause-and-effect analysis evaluating the impact of the published information on the value of Thomas Cook’s stocks is carried out. The general lesson for companies resulting from this contribution is that every negative event, announcement or piece of information has a negative impact on the value of a company’s shares and a collapse could happen even to the leader of a given industry. The collapse of Thomas Cook provides lessons for companies doing business in tourism, so that in the event of a planned merger, a suitable company is selected, the company’s funds are under control and development trends in the field are monitored.