Like many of the previous replies, a lack of communication and time has been one of the most prolific problems in the projects I’ve worked on. In one such project we had made an initial WBS that we would have updated as we gained knowledge of the processes we were working on, but as time went on we had forgotten and put it on the back-burner. This resulted in a mad scramble towards the end of the timeline where we kept running into new tasks that we had to do but did not expect. We did end up finishing albeit with much less features than we initially hoped. Really good planning cannot be neglected.