Humans have many instincts, innate. Naturally, people can understand it. There is no need for Qur'anic Hadith or any other documentary evidence to explain it. Such as eating on hunger, drinking on thirst, seeking medical attention in case of illness. Why eat if you are hungry? Why do you have to drink thirsty? Why do you have to seek medical help? No different documentary evidence is required to explain this. These are human nature. People understand by nature. On the contrary, if one of them seeks evidence, people will laugh at him.

Again there are some things that are not innate. It is not understood by nature, but requires different documentary evidence. For example, will the muqtadis recite Surah Fatiha in the prayer? Will he raise his hand in prayer other than the time of Tahrima? Etc. There is no way to understand these by nature. These have to be understood with the evidence of Quran and Hadith. Obedience to madhhabs, taqlid practice, development of madhhabs and taqlids, etc. are also matters of nature, not matters of documentary evidence. People seek medical help for illness. It is natural, in the same way that people take refuge in a wise person to know the religious masala-masayel. It is also innate.