One of the problems we all have is that life sometimes gets in the way of our plans.
For speakers that can be troublesome. When you wait to the last minute to practice, it shows. It also maybe be as simple as wanting to show a few photos during your presentation but they do not arrive in time. When you wait to the last minute to practice without the photos, it can be difficult to adjust for the absence of the photos. You may have thought previously that this is a good place for my photos and label your notes accordingly but then the photos do arrive. Since it is the last minute you now have to relabel your notes and you are being rush for time. Being rushed is an excellent recipe for missing something.
Everyone thinks that they have enough time for whatever activity they are trying to accomplish. Just remember, life has a tendency to get in the way. Start early.