It does not mean when you know how to write a song you can be a singer! I know a person who is so proud that he had written 10 songs, he needs 2 more to compile a CD. He invited me to his link to listen and like the song that he wrote and sung. I did click the like button just for the sake that we're friends.
His don't have the voice of a singer although he can write songs, while listening I'm like "Oh GOD hope he will realized in his own that he couldn't sing. I'm having hard time understanding his lyrics cause he's like murmuring. Oh boy I wish people will know what they can and CAN'T do in life so they will not embarrass themselves.