Why can't I look at the sun?

I distinctly remember my grandmother nagging me from her driver seat while I sit in the backseat staring out the window at dusk, "Don't stare at the sun; you'll go blind!"  I hear this time and time again, but no one ever tells me why it'll make me go blind...

Will the UV rays overwhelm my sensory neurons and cause them to go on the fritz and then stop working?  Will the intensity of the sun penetrate my occipital lobe like a laser?  Will it melt my eyeballs?  Will it just cause so many dots in my vision that they'll never go away and I'll never be able to see normally again?

As I desperately try to look at the solar eclipse tonight, these are the questions that run around inside my brain.

The best answer I found when I googled my question was posted by Elizabeth H. on Yahoo! Answers:

"The solar radiation that reaches the surface of the Earth ranges from ultraviolet (UV) radiation at wavelengths longer than 290 nm, to radio waves in the meter range. The tissues in the eye transmit a substantial part of the radiation between 380–400 nm to the light-sensitive retina at the back of the eye. While environmental exposure to UV radiation is known to contribute to the accelerated aging of the outer layers of the eye and the development of cataracts, the primary concern over improper viewing of the Sun is the development of retinal burns.

Exposure of the retina to intense visible light causes damage to its light-sensitive rod and cone cells. The light triggers a series of complex chemical reactions within the cells which damages their ability to respond to a visual stimulus, and in extreme cases, can destroy them. The result is a loss of visual function, which may be either temporary or permanent depending on the severity of the damage. When a person looks repeatedly, or for a long time, at the Sun without proper eye protection, this photochemical retinal damage may be accompanied by a thermal injury—the high level of visible and near-infrared radiation causes heating that literally cooks the exposed tissue. This thermal injury or photocoagulation destroys the rods and cones, creating a small blind area. The danger to vision is significant because photic retinal injuries occur without any feeling of pain (the retina has no pain receptors), and the visual effects do not become apparent for at least several hours after the damage is done (Pitts 1993). Viewing the Sun through binoculars, a telescope, or other optical devices without proper protective filters can result in immediate thermal retinal injury because of the high irradiance level in the magnified image.

The only time that the Sun can be viewed safely with the naked eye is during a total eclipse, when the Moon completely covers the disk of the Sun.
Source(s):
NASA"

Thank you, Elizabeth H.  Now I understand the seriousness of the situation, and I really won't stare at the sun anymore.