When enabling the flash (by deploying the built-in, pop-up flash; or by using the hot shoe with an external flash device) the apparent brightness of the image displayed on the LCD monitor (LiveView) and/or electronic viewfinder (if it has one) automatically increases dramatically.
In some situations, the frame will be too dark to compose a shot, so I will pop up the built-in flash, and straight away I can compose a nice, sharp image. And then of course the flash fires as the shutter actuates, and it ruins the shot.. Cover up the flash, and it turns out darker than the preview.
But the thing is, I already had the desired image in the buffer, and displayed on the screen. It already existed. I saw it. The camera saw it. But I was unable to keep it. How do I get that exact image, as is? It's like it's trying to do some fancy exposure simulation business, and shooting itself (and me) in the foot.