I just bought and install Minecraft 1.8.3. I then ran it and started a new world, saved and exited.

 

I then downloaded installer for Forge 11.14.1.1337, and ran it. It tells me I need to run 1.8 first, and exits. I have verified its path to minecraft is correct, /Users/adam/Library/Application Support/minecraft.

 

The installer does not generate any log file that I've been able to find.

 

Here is the "latest" log from Minecraft:

[19:05:29] [Client thread/INFO]: Setting user: adameros

[19:05:29] [Client thread/INFO]: (Session ID is token:4c61cf446fae4c37a11c728c638122c5:9c394f1c77c14ab1ad3d4d17ce15779b)

[19:05:33] [Client thread/INFO]: LWJGL Version: 2.9.2

[19:05:34] [Client thread/INFO]: Reloading ResourceManager: Default

[19:05:34] [sound Library Loader/INFO]: Starting up SoundSystem...

[19:05:35] [Thread-12/INFO]: Initializing LWJGL OpenAL

[19:05:35] [Thread-12/INFO]: (The LWJGL binding of OpenAL.  For more information, see http://www.lwjgl.org)

[19:05:35] [Thread-12/INFO]: OpenAL initialized.

[19:05:35] [sound Library Loader/INFO]: Sound engine started

[19:05:42] [Client thread/INFO]: Created: 512x512 textures-atlas

[19:05:44] [Client thread/ERROR]: ########## GL ERROR ##########

[19:05:44] [Client thread/ERROR]: @ Post startup

[19:05:44] [Client thread/ERROR]: 1281: Invalid value

[19:05:44] [Client thread/ERROR]: ########## GL ERROR ##########

[19:05:44] [Client thread/ERROR]: @ Pre render

[19:05:44] [Client thread/ERROR]: 1281: Invalid value

[19:05:53] [Client thread/INFO]: Stopping!

[19:05:53] [Client thread/INFO]: SoundSystem shutting down...

[19:05:54] [Client thread/WARN]: Author: Paul Lamb, www.paulscode.com

 

What am I doing wrong?

You need to run 1.8 not 1.8.3 you can change your version in the edit profile screen.