I worry that simple is equated with easy too often.
Too often I see people mistake the output for the process. It can take years of sifting through data, asking the right (and wrong) questions, or trying lots of things to arrive at an answer. And sometimes, after all of that, the final answer could be expressed in very few words.
Just because something can be explained simply doesn’t mean it has taken no effort to get to that explanation. If your ideas or research seem simple to explain now, don’t worry, your examiners will understand how you got to that point.
And if you find something easy at the end of your PhD, it can still be incredibly complicated – it could be too hard for other people – but not for you. Not at the end of your PhD.
Remember: simple and easy are not synonyms for each other; nor are they synonyms for worthless.