A useful model for figuring out how fancy you can be
You have probably already come across, or made use of, the BJ Fogg Behaviour Model. Basically it's a behaviour model that claims that three elements must converge at the same moment for a behavior to occur: Motivation, Ability, and a Prompt.
I like it, and I use it quite a lot, but it does have its problems. First of all it includes maths. It literally has its own equation: B=MAP. I understand the purpose of expressing the model as an equation, but it makes it feel like it's more precise and reliable than anything to do with human behaviour can probably aspire to be. However, it is a useful way to frame up behaviour design problems, as long as you treat is as an approach rather than a rule.
For myself, I don't primarily use it as intended. I more commonly use it to get an initial feel on how complex I can make a system. I take the maths off the graph, but include the main components; motivation and ability. When you do this, you can plot an approximate level of ideal complexity, for example a dense and complex system (think an airline cockpit) for a high motivation / high ability person, or a simple system (think google.com) for a low motivation / low ability person.
If your research gives you a reliable approximation of your user’s motivation and ability, you can plot these and use it as a way to think about if you should focus on increasing or decreasing the complexity of your system to meet their needs, if you should concentrate on increasing the ability (through education) or motivation (through behaviour design) of your user, or some combination of the two.
Sometimes it’s easy. A user who needs to achieve a complex task such as financial trading benefits from a powerful and efficient system that facilitates their trading, even if that does make the system more complicated (such as a Bloomberg terminal). They are also highly motivated, they will invest time and energy into learning that system.
Sometimes it’s more nuanced. A photography post production professional will also benefit from a powerful and efficient system (such as photoshop) but has other options. Some photographers have opted for less complex systems as they can achieve the results they need with less investment in learning a complex system (for example Lightroom or even Canva).
It’s not science, but plotting this out is a very useful way to guide and focus your own thinking and conversation with collaborators and stakeholders. No maths required.
Modified (and flipped) version of the BJ Fogg Behaviour model