"Simple" is the opposite of "complicated".

"Easy" is the opposite of "hard".

Reaching a high shelf is very simple. But if you're short, it may be hard.

Calculus is very complicated. But if you're a third-year grad student in mathematics, it may also be very easy for you.

Simple and easy are not antonyms here -- something can be simple but difficult to accomplish depending on the time and place at the same time. For example, "respect women" is a simple enough phrase but getting the Taliban to follow it is anything but simple.