In the 21st century, distinction between the two forms of definite article is diminishing in informal speech, a change impelled partly by the influence of young second-generation immigrants.
There is precedent for this shift in the Surinaams-Nederlands dialect and in Afrikaans, both of which have only one bepaalde lidwoord.
A peculiar feature of the Dutch language is that it employs two definite articles.
De and het both mean the same thing "the." But any noun is correct only if correctly matched.
There is a rule, but it's based upon "gender," and the average noun has no gender-identifying characteristic.
Semi-arbitrary gender affiliation systems of nouns is not unusual. Nouns in much of Europe have a "gender" assignment that is not semantically logical. But there are rules regularity, and predictability, in Spanish, for example, where the form of the word indicates gender so the definite articles are generally easy to use.
In Dutch you can't tell whether a noun is masculine or feminine. But, stranger yet, that's not what matters: what matters is whether it's either or neither. The definite article for all gendered nouns is "de." For the neuter, it is "het." (In addition, het is used for all nouns in their diminutive form, analogous to the Spanish "ito / ita.")
So, the critical matter is whether or not the noun has a gender. And it is this which is invisible and inaudible most of the time. There is a sense amongst the Dutch that they "just know" whether "de" or "het" is correct. This does seem to be true, but the grasp of usage is probably formed in childhood rote learning. Some claim that the native Dutch speaker would even know which definite article to use with a nonsense word. That doesn't seem possible, and is probably not true.
For the student, the foreigner, there is one general rule, not very elegant. You have to memorize each noun's definite article. There are some groups for example, the names of animals, languages, and colors within which the usage is consistent. But that's it. It's a memorization task.