Don't Understand what I am doing wrong : Can someone help?

[meekschr]

user=input("Hello, I am the computer. What is your name? : ")
print("Hello,", user)
user=input ("Chris, do you enjoy programing? : ")
if "yes" :
print("I enjoy it as well. I happen to run on programs")
else :
("Why not : ?")
------------------------------------------------------
Hello, I am the computer. What is your name? : chris
Hello, chris
Chris, do you enjoy programing? : no
I enjoy it as well. I happen to run on programs

Process finished with exit code 0

I don't understand why the computer does not respond with "Why not : ?"