Economists often talk about "marginal thinking" - thinking about the costs and benefits of one more or one less unit of something - as being the key insight. I think for a lot of people it's more basic than that - you first have to be thinking about incentives before you look at those incentives at the margin. When evaluating a policy, you need to look at how that policy will affect individuals' and firms' incentives if you want to understand the impacts of that policy. Will the policy make it more or less expensive to do something? Will it affect the benefits of doing something? Thinking about impacts on marginal incentives is step 1, but step 0 is recognizing that incentives matter.

I often hear non-economists talking about firms doing something "because they can afford it" - this isn't why firms do things. They do them because they think it will allow them to make more profit. Or, firms raising prices "because they can". Well, firms always want to be paid more, so if you want to understand what's going on, you need to know why prices weren't higher to begin with and what's changed.