Step 1, the source
Say your car comes with an advanced electronic system (computer chip) that handles the fuel/air ratio and other stuff like ABS, headlights, tire pressure, etcetera.
A lot of programmers worked hard programming that chip and they consider themselves as the author of their programming. The code is theirs. They want to sell it to car companies to make a living. They love cars. They love making it safe. They love they can make money with their passion.
Step 2, making money!
They sell this chip, with the code, to some major car manufacturers, which happily pay the license fee and install that thing in their cars. The manufacturer is happy. The chip checks everything and the car works perfectly. This investment will benefit the company.
Step 3, it's mine!
Now you suddenly decide to build or modify a car yourself. You are not in the mood to buy a licensed chip and can't really get the hang on how to handle the fuel/air ratio, ABS, headlights, tire pressure, etc. But you know of this chip from another car. You copy the content of that chip to another chip using a programmer and install it in your car. Much cheaper.
Step 4a, sale!
Now you sell that car to your customer.
Step 4b, happy hobby!
Now you give away the method of making your own chip to your friends. They all can make cheap chips now.
You may think there is nothing wrong with this. Perhaps there isn't anything wrong with it.
Now re-read the story and pretend you're the programmer.
Now re-read the story and pretend you're the car manufacturer
Feeling screwed yet?