Here is the shoe-size data for 9 students in our class. Change the shoe size of one student (★) with the slider and see how the mean, median, and mode respond.
The mean is found by adding all the values and dividing by the number of values, so even one extreme value (outlier) can affect it a lot. The median is the middle value when the data are ordered, so it is not easily affected by an outlier. The mode is the value that appears most often.