There are many reasons why data science projects fail. You can find out more from the slides of Daniel Meister’s presentation series entitled “Digital Shift”.
One thing is clear: a lot can go wrong in the initial phase of a business analysis, often because the focus is wrong. The question must therefore always clearly be: “Where can we actually optimise our (core) business further? What additional information do we require for this? Do we have a realistic chance of getting this data?” The complete summary of the event can be found under Digital Shift. You can download the presentation here.