 What if you have to conduct a forensic engineering investigation and someone asks you that cringy question, are you sure you have considered all possible causes? Now, did you? And how can we ever be sure to have considered all possible explanations of something that went wrong with a complex technical system? And can we always be sure we did not miss the cause we were looking for? Actually, perhaps we can't. But if we use a well-defined diagram of all kinds of causes that could be related to the failure of technical systems, we could at least use this as a kind of checklist to see which ones are likely to have occurred. But what should we use as that diagram? Well, we're going to use a treehouse for that, and I hope this one was developed and produced sturdy enough to allow me to get down safely again. Consider the proper functioning of any technical system to be a treehouse. The treehouse is supported by a foundation consisting of carriers, which are beams that span horizontally to carry the floor. Each carrier is supported by a set of three stems that all grow on a bunch of roots hidden underground. The treehouse will collapse if the foundation caves in, when anything in that foundation system breaks. As a simple drawing, it would look like this. Three carriers resting on their stems, which are firmly held upright by their roots. Now from this drawing, we go to the treehouse of failure diagram. This diagram describes the foundation of the proper functioning of a technical system. Such as a treehouse.