Not intentionally being pedantic, though it will seem that way.
My biggest gripe with this is that "the trick to x" changes repeatedly. The article is title "The trick to spending money wisely", then immediately changes to "Spending money wisely is the trick to building wealth." These are two entirely different things. Not much further along, it changes again to “The trick to becoming wealthy is to become aware of which category the majority of your income falls into.” But then, the way to become wealthy changes in another couple of paragraphs to this: “The way to wealth is simple. You become wealthy by allocating the highest percentage of your income toward making investment category purchases.”
In all, these don't detract from the article, but with the premise of the article starting as a trick to spending wisely and ending as the path to building wealth, it lacks an internal consistency.
An actual trick to spending wisely might be something like "for each purchase you make, stop and consider whether you will still get joy or use from this item xx days/weeks/months/years from now." Or maybe another common one "only purchase items which will have a long term net cost of $1 per use. For instance, a $20 shirt will need to be worn at least 20 times to justify the expense."