Proprietary software

Friend: I've heard about "free" and "proprietary" software... Why do you call "proprietary" the non-free software?
Programmer: It's simple... Because when you buy the software, in a weird way, it becomes your proprietary... He owns you!
Friend: But if I bought it, i'm the owner!
Programmer: Really?? So, who defines how will you use the software? Or on how many computers you can use it? Or if you can update it? Or else, who chooses if you can know how it works inside...