Decision-making is defined as the process of choosing between a minimum of two or more options or variants when solving a problem or a dilemma. This process takes some time and ends with the decision itself. Decision is a choice within several possible solutions to the problem and is also the outcome of the decision-making process. Business decision-making is decision-making in business situations within the company and its environment. There is no decision-making process, whether it is personal or business decision-making, that can be rid of mistakes. There are 10 most common mistakes in decision making: ignoring problems, accepting the first solution, persistently using old solutions, looking for the perfect solution, overconfidence, and optimism, supporting a once made decision, resilience of belief, representativeness error, availability error and presentation method. The most common and most serious decision-making errors that have their source in the decision-making process are decision-making on the wrong problem, misidentification of key criteria and goals, defining inadequate versions, ignoring the consequences of defined versions, ignoring uncertainty in decision-making and ignoring decision-making. Also, among the mistakes in decision-making can be included the use of the wrong style of decision-making in problem solving. Mistakes in decision-making caused by the way decision-makers think are also called psychological decision-making traps. Some of the most common traps are the anchoring trap, the sunk-cost trap, the status quo trap, the confirming-evidence trap, the framing trap, and the estimating and forecasting trap. Decision makers should be aware of possible mistakes / traps and follow the recommendations given in the paper to avoid them. Through the example of the Thomas Cook agency, the paper analyses some typical mistakes in decision-making in business practice.