For Mecanim to produce a valid match, your skeleton needs to have at least the required bones in place. The inspector shows which of the bones are required and which are optional - the optional ones can have their movements interpolated automatically. Once you have saved the scene, you will see a new Avatar Configuration inspector, with a bone mapping. The reason for this is that in Configure mode, the Scene View is used to display bone, muscle and animation information for the selected model alone, without displaying the rest of the scene. When you go to the Configure … menu, the editor will ask you to save your scene. Here, success simply means all of the required bones have been matched but for better results, you might want to match the optional bones as well and get the model into a proper T-pose. If it succeeds, you will see a check/tick mark: If the automatic Avatar creation fails, you will see a cross next to the Configure button. It is important that your character’s bone structure matches Mecanim’s predefined bone structure and that the model is in T-pose. So, whether the automatic Avatar creation fails or succeeds, you need to go into the Configure Avatar mode to ensure your Avatar is valid and properly set up. Since the Avatar is such an important aspect of the Mecanim system, it is important that it is configured properly for your model.

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