The "Portfolio" tag represents my personal selection of what I consider to be my best work. Which pieces make or don't make it into this list may at times seem confusing - The reason for this is that, as opposed to a casual visitor (who might simply ask "Which artworks are the prettiest?"), I make the decision to include (or not to include) a piece in my portfolio based on three specific evaluation criteria:
1) The quality of the piece has to be on a high level, but the same does not necessarily apply to the level of elaboration, the time invested, or the amount of rendering detail (all criteria commonly associated with "good" art by non-artists).
2) How closely does the end result resemble my intended goal? The notion of "control in art", in the sense of not only being able to produce pretty (but random) artworks, but to precisely control what the finished artwork looks like, is very important to me. I don't like to leave my art up to chance.
3) In some cases, the fact that a certain piece was unusually difficult to make (on a technical level) also contributes to my being proud of it, and qualifies that piece as a portfolio piece because it represents a technical achievement, even if those technically challenging aspects are typically not apparent to a non-artist visitor.
Even a rushed sketch may at times fulfil these criteria, and even a large-scale project which, to a casual onlooker, seems to easily qualify for a portfolio, may turn out not to fulfil them - Indeed, the larger the project, the more likely it is there are aspects of it which I'm not happy with.