Ubiquitous means something existing or being everywhere at the same time, a synonym is omnipresent.
Confusing refers to something that is not easy to understand because of it's complexity or lack of organization or explanation.
Therefore something that is ubiquitous is often unattainable for our reasoning, that means it becomes confusing for us, as we can't adapt it easily to concepts we can manage. Our minds can't understand everything at the same time, our brain needs to catalog and prioritize information to understand it. Imagine going to the cinema and sitting at the very front, the images are so close to you they appear to be everywhere you stare, sometimes that confuses you as you try to focus on a spot missing a lot of things. This also happens with nature, that is the reason science is divided into different disciplines; and with concepts like God, it is difficult to imagine a being that is everywhere at the same time but that can't be seen, it leads to a lot of confussion and various attemps to explain it.
Low-fidelity prototypes are often paper-based and do not allow user interactions. ... High-fidelity prototypes are computer-based, and usually allow realistic (mouse-keyboard) user interactions. High-fidelity prototypes take you as close as possible to a true representation of the user interface.
