You always wash the dishes after you used them and most likely you always iron and fold your clothes before you put them into the closet. You don't signal to the left when you turn right, and you don't go through the red light and stop at the green light. You start the sentences with capital letter and end them with the proper punctuation mark.
Some of these examples are only habits, others are forced by some law, yet another is only a matter of following some rules. What they have in common is that they're only conventions and as such they're are all breakable. What happens if you intentionally break these habits, laws and rules? Hopefully nothing serious, and everything goes on normally. On the other hand... You can put your crumpled clothes into the closet but when you wear them you'll look austere. You can cross the red light but you endanger your and other's safety. You can start a sentence with lower case letter but other's may think you're uneducated. You don't want, of course, any of these to happen, so you don't do these things. You simply follow the rules and habits because you know that's the way to do it.
The same principles are true when it comes to clean coding. You don't want others to clean up your mess. You format your code, so it's nice to read. You don't call your method
addwhen it does subtraction. You don't call
false. And you don't start a class name with lower case letter, or a method name with capital letter. Why? It's obvious. Because only applying the industry standards ensures that you don't make your colleagues' life harder when they have to read, understand and maintain the code you wrote.
For most of us it's common sense. It goes without saying or without thinking. We learned these conventions, principles and rules and use them all the time without making extra effort or wasting time. But unfortunately there's always a few exceptions whose concern towards the code ends as soon as it builds. The code they produce is syntactically and semantically correct, though, but the hair on the back of your neck stands when you have a look at it. When I see such a code I often wonder if the author of the code is as negligent in other aspects of his life as much he was when he wrote the code, or it's only his indolence that prevented him doing things on the right way...