We said above that bipedality was a characteristic of man. But if your analysis included all groups of mammals, you would probably note that kangaroos are also bipedal. Intuition tells you they should not. This problem is handled by including as many different characters as possible in a cladistic analysis. When one, like this, clearly doesn't fit the pattern of all the others, it is assumed to be an anomaly and overridden in the analysis.
Reversals can cause problems, too.
We said above that all mammals have fur. Again, when anomalous characters like this are encountered, they are overridden in the analysis. It is important to use enough characters in the study that things like this will shake out. Another problem arises when dealing with fossil material in that sometimes parts of the animal are missing which are needed to evaluate a particular character. This problem is handled by gathering data on as many characters as possible so that no one deficiency is likely to throw the analysis off.