Every week there's a few really important tasks that I forget. There may be too many tasks or just a few really time consuming assignments, but the bottom line is that there are always things that I can't remember, irrespective of their importance. I rarely miss deadlines with such forgotten tasks though, largely due to having a tasks management system. Without assuming that you already have such a system, I'd like to draw your attention to the important of not only having a system but also making sure that's a system you can fully trust.
Does everyone really need a system to manage tasks?
Depending on the number of daily incoming tasks, you may get away with having no system for managing them. But as soon as the number of tasks becomes overwhelming (you'll be surprised how small this number needs to be!), you'll start forgetting tasks or delaying their completion due to last-minute change of priorities.