Whenever I've helped older people with technology they've never used before (a new tablet or similar), if I started off with any suggestion that it's less than simple, they'll almost certainly frame the problem scope in their mind as difficult, and give up, because they're already exhibiting some animosity toward learning a new thing.
If instead you phrase it as "this is really easy, let me show you how...", you short-circuit this process by framing their expectations differently, and that little bit of extra confidence ("this is easy") can help them through the learning process.
I've found you can't simply show them, either. It's almost better to say "It's easy" and then go through the process, because it's absolutely necessary to establish expectations first. They're already afraid of it (it's new), so doing something to get their guard down can go a long way toward helping them explore on their own. I tried this experiment with my mother, and some weeks later she'd have a problem and discover the solution herself specifically because she was convinced it was easy to do. This can (and will) backfire if you're not careful about how you do it, but I've had far more success using this tool than other techniques individually (e.g. writing down instructions).
This doesn't broadly apply to areas outside education and support (or even to all areas in education), but for simple things that people may express an irrational fear over, it works and it works well. A good teacher will use this technique successfully with their students, so if you're teaching someone, use it!
If someone has some anxiety about not understanding something, telling them it's actually pretty simple can just reinforce the framing they already have going in that maybe they're too dumb to get it.
I've found it's usually better to acknowledge that it's a little difficult or otherwise totally normal not to already know / have grasped the thing in question.
I think the intent is in the right place when saying "it's actually pretty simple" -- you want to provide optimism. The approach I like is along the lines of "this part is a little tricky, so let's break it down."
I punched "It's actually pretty simple" into http://talktotransformer.com (which generates nonsense text from a seed using an OpenAI language model) and after a couple of tries it gave me this:
> It's actually pretty simple. We'll be looking at something called the "D-Wave P-500", which is a version of the P500 chip for quantum computers.
> It's basically a single bit computer, but with more than 500 qubits. Which means that our "real number" will have more numbers than the number of qubits that are available. That's really important.
> Quantum computers are theoretically able to do more things than just solve equations. For example, the way that a quantum computer uses energy from an electron to solve a classical math problem, or the way that it can break a complex calculation into smaller bits of information that each can solve on its own, is very different from how computers currently work.
> But I am not suggesting that a quantum computer can be used to solve more abstract problems. Because that would be crazy.
> But to give an example of what it could do, imagine doing a number crunching function that was 10× faster than a classical chip, and that had some really useful, and practical things that would be interesting to try.
Because Talk to Transformer is trained on real-world data, this supports the hypothesis that the phrase "It's actually pretty simple" is often followed by an unintelligible and highly technical explanation.
Humans generally are afraid of new words (especially weird sounding ones) and often will assume that the subject is complex and might intimidate them.
But unknown words can have extremely simple meanings, or be synonyms of already known words.
By asserting: "It's actually pretty simple" You give them confidence that there's not reason to be afraid of the topic or of the words.