What is a "good picture"?

Translated from a gem found on bilibili, in a note-to-self format.

Before an artist starts, you can bet that they had (1) an idea of the effect they would like to achieve, which for sure was based on (2) an impression of something they saw or experienced. If they were successful in (re)creating that effect/impression, they will think, "this looks good". Any audience who similarly likes the same (2) impression/look will also think, "this looks good". At that point, the piece is a success. It is that simple.

What we mean by (2) is not a specific image, but an established pattern/formula. Therefore, when a picture "does not look good", it simply means it failed to properly match any pattern or formula. Conversely, if any formula/pattern is correctly applied, the picture will  "look good". Furthermore, the same base image can be edited to create multiple looks, each following a different formula, and all of them will "look good".

Some examples of patterns/formulae (screenshots from video): 

 I. Environmental/Atmospheric: dark subject, light background, bright rim light

 

This is prob the most common one in digital art these days and can be seen when atmosphere and mood dictate the piece, e.g. League splash art. Environmental light overrides local colors. Multitudes of looks/moods can be created branching from this basic formula. 

II. Classical: light subject, dark background, bright rim light

 "Classical" in the sense of old timey portraits, e.g. Sargent. Commonly seen in character-centric situations such as character sheets, card illustrations, etc. Local colors remain bright and clear. What if you want to do a daylight scene where the sky is bright? Simply use blue (which, inherent to the hue, has the darkest value of all hues). 

But the above are simply the level 1 basics. At level 2, we can mix and match between the above two broad rules by introducing new lights.

In these more complex lighting scenarios, it becomes mandatory to change up your background to constantly contrast with the subject/foreground. Above the +++ line, we have bright foreground/dark bg. Below the line, things flip to dark fg/bright bg. Bg always needs to serve the fg through contrast.