Here's why a can opener can be considered simple**:

* Few moving parts: Most can openers have only a handful of components: a handle, a gear, a cutting wheel, and a mechanism to hold the can.

* Basic function: Its primary function is to cut through a metal can, a relatively straightforward task.

* No electronics: It doesn't rely on electronics or complicated systems.

However, here's why a can opener can be considered complex**:

* Precise mechanics: The gear system and cutting wheel need to be carefully designed and engineered to work together to create a smooth, controlled cutting motion.

* Material science: The cutting wheel needs to be made from a material that can withstand the pressure and friction of cutting through metal.

* Ergonomics: The handle and grip need to be designed for comfortable and efficient use.

Overall: A can opener is a simple machine in terms of its basic design and function. However, there are some subtle complexities involved in its engineering and mechanics.