A machine can also become intelligent if it is trained with data which helps them achieve their tasks
For better efficiency of an AI project, the Training data needs to be relevant and authentic. For example an AI modal can predict the salary of any employee based on his previous salaries, you would feed the data of his previous salaries into the machine. This is the data with which the machine can be trained.
For any AI project to be efficient, the training data should be authentic and relevant to the problem statement scoped.
if the training data was not of the previous salaries but of his expenses, the machine would not have predicted his next salary correctly since the whole training went wrong. Similarly, if the previous salary data was not authentic, that is, it was not correct, then too the prediction could have gone wrong. Study more about introduction to AI at intro to AI