Before you read any further. I'm not being paid by Guess for posting an image of their denims. They may or may not ever find out about this post. And the subject I'm writing about has nothing to do with the brand either - so my intention isn't to cast a particular image towards them, either positive or negative. So now that the air is clear, lets get started....
Guess work. Thats what it it when you don't know what you're doing. It's like walking into a rocket science class as a 16 year old thats still in school. It happens as well the first time you start using a DSLR. The first few times actually. It took me a solid 2 - 2 1/2 years to fully grasp the sheer computing POWER of my DSLR. Practice, practice, practice. I put myself in different situations. Often. I used to shoot band gigs on Friday and Saturday nights in order to see different results of the lights, the shadows, people etc without using flash in the situation. I practiced the Sunny 16 rule out in open. I tried shooting in aperture priority with my aperture set to 32 or 36, and adjusted my ISO/ASA in conjunction with shutter speed to see the results (a tripod was useful here - I used the self timer for a few years, and finally bought myself a shutter release cable).
I pushed boundaries to experiment with film, played with pushing and pulling film (and made a few mistakes here), and also Photoshop. Photoshop Photoshop Photoshop. Looking at different techniques my friends use too get similar results, and seeing how stuff can get added and subtracted....its probably safe to say that I, as well as many others, will probably never tap the full potential of Photoshop. If you do, it'll be after 10-15 years experience, or you'll be a graphic designer that edits other peoples images (this comment may blow a few egos, but its true. Just accept and move on here).
And you know what? I can't explain how the electronics in my camera work. The early photographers probably didn't have an exact idea on how their cameras worked either. But they knew that specific techniques gave specific results. I like to think I'm the same - I have different cake baking recipes. A very good idea on how to set my camera for low light settings, high light settings, etc etc. This helps me keep enhancing the images (note how I didn't say 'edit'- it implies that the image was crap and you needed to fix it) to a minimal.