When analyzing data, be critical and ask questions. Data should make sense and it should fit into the bigger picture. If something doesn't make sense, figure out why. Sometimes data is wrong and has quality control issues. But sometimes the data is correct and it's trying to tell you that your assumptions are wrong. Engineering problems require fitting the data together like puzzle pieces. If a certain piece doesn't fit, figure out why. Don't just throw it out because it threatens to debunk your hypothesis.
If something doesn't make sense, ask yourself why. This is a good rule of thumb to follow in both engineering as well as life in general.