Complexity is the province of engineering. A prime purpose of engineering is managing complexity. One of the primary tools of doing this is multiple levels of abstractions.
The level of abstraction you use is selected by the task you are attempting. This allows you to focus your attention at the level and on the information that you need to accomplish the task.
Example: Suppose you want to understand traffic patterns on a highway. It is unlikely to be useful to attempt to do it through the principles of quantum mechanics (QM) and the interactions of atoms and molecules. Yes, as PeterJ mentioned, at the level of principles, physics is simple. The rules that guide QM can be stated on a t-shirt. But that is unlikely to be the best way to understand how to design a highway interchange. This is the case even though QM is indeed the fundamental basis on which the traffic patterns are built.
However, if you attempt to understand traffic patterns based on the behavior and capability of individual cars and drivers, you are much more likely to get some kind of useful answer.
Another example: Suppose you want to understand the correct operation of the video record feature on your brand new smartphone. It is unlikely to be useful to start at a discussion of the electronics and such that go on inside the phone. It will be distracting from the task.
Another example: If you want to bake a cake, you are unlikely to be happy by starting with the theory of gravity and the motion of planets. Even though it is gravity that keeps your cooking materials resting on your kitchen table, that isn't the place to focus your attention. You are going to be a lot happier with starting with a recipe and some understanding of how to operate your oven.
And an example with a built in reference: If you want to explain how to make a really good cup of tea, it is unlikely that the best plan is to start with a history of the East India Co. It will, for most circumstances, be a huge distraction.