What was the most important decision you ever had to make? How did you arrive at that decision?
An important part of assessing your skills and personal character is to test your behavior towards trying or challenging situations. This is another type of behavioral-based questioning in which your answer is tailored from personal experiences as the interviewer's basis of your future performance in case they will consider you for the job. Employers would want to guarantee that the potential candidates they choose have good decision-making skills. A person who is able to make sound decisions when prompted with the need to do so is reliable enough to self-supervise without having to consult the immediate superior from time to time regarding decision-making matters.
When your interviewer asks this question, the mind starts to sort through a series of experiences in your life that mainly involve decision-making. Most people's problem is in controlling their train of thoughts. The idea is to limit your answer to only one decision-making experience that you consider as major or important. In addition, that experience has to be a positive one instead of choosing the unfortunate moments you went through. Share a major decision you made which did not only create an impact on you personally but also affected that of the others or a situation in a good way. Personal or work experience will do, as the focus of this question is your ability to make a personal decision out of the situation.
Interviewers are not just content on a simple answer especially if a question such as this requires you to support it with a sharing of experience. After highlighting that major decision from either a personal or professional experience, make it a point to elaborate further on why you have to make such an important choice at that time and how you came up with the decision. But refrain from providing a lengthy explanation; you do not want to bore your interviewers with your overly detailed story. If there is a need to mention certain individuals who have helped you arrive at such decision in one way or another, then do so. Make it clear that you simply heeded their opinions but not to the point of taking their suggested choice for you.
Close your short speech with an emphasis that you have greatly learned from individual decision-making and that such experience has honed your ability in making decisions. Give your interviewer the idea that you can be trusted when it comes to making choices such as knowing which task to work on first and which task is less urgent. When you leave this impression that you simply know what do without being told, you have just given yourself an edge over the other candidates. Always wrap up your response in a highly positive manner. You can close it by telling them that you are being frequently consulted by people at work or at home for decisions.