I don't struggle to understand them, exactly, and I certainly understand how people can spend all that money. What I do struggle to understand is why some professions pay so much in the first place. (I don't mean roles in medicine, some types of law, or other professions that contribute to society as a whole - though they tend not to be the really well paid roles anyway.) I particularly struggle with the differentials when you look at how badly paid care workers, or classroom teachers, or some of the uniformed services are, for instance, or other roles that keep society running, like hospitality, production workers, delivery drivers etc.
I also really struggle with the sheer lack of imagination and empathy that some (not all) of those earning these salaries exhibit. This is especially the case when it comes to understanding how difficult it is for people with the "average" income or below to survive. It's not like you get special lower energy rates or anything when you're poor; and as a percentage of your income, it has much more of an impact. That £20 a week that the government and some of its supporters are so snarky about for instance? That's probably a tiny glass of wine or a gilt-encrusted breakfast crumpet to them, but for some people it's the difference between being able to feed their kids or feed the electricity meter.
And where I REALLY struggle is when (some, not all) people with those incomes say things like, "Oh, but I worked so hard" - like poor people don't?! And often don't appreciate just how much their income is due to luck/family inheritance/their grandparents having bought a house for £100/being clever enough to be born into a wealthy family with good connections/go to the right schools, universities, etc.
What's that meme again, the one along the lines, if hard work was genuinely rewarded as it should be, every poor village worker in Africa would be a millionaire...