We can keep this page very short. The number one reason why top artists produce such high-quality and consistent series is curation. They cull anything that doesn't match their standard.
It's easy to get emotionally attached to a photograph for very good reasons: maybe the circumstances in which it was made. Or maybe it was the first time you achieved a specific look you were after. Or maybe it depitcs someone you love.
That doesn't make it a photograph you can sell.
Reasons for excluding photographs from your official portfolio are numerous and not always linked to quality.
Sucessful artists recognise they are brands. Anything off-message hurts the brand. Of course, that's not necessarily present in their mind when creating their work. Building a brand was probably the least important consideration to Jean-Michel Basquiat, for example. And no meaningful artists creates work specifically to build a brand (notice the word meaningful. Some very famous artists do exactly that, but not all can be considered particularly interesting from non investment related points of view). But the fact remains that artists are brands in that they create expectations.
Anyway. Create what you like. But be very strict with what you pick to sell. That's what (some) galleries do for (some) artists. Better still, as in Phr, ask other artists to help you with that selection.
Let's consider the photograph above. It's a good photograph of an alpine lake. I processed in in Sepia because it reminded me of the first survey photographs, such as those by Timothy O'Sullivan.
Can I sell it? Not if all my other photographs are in colour. Or if I never sell anything about nature. Or even if I never print in sepia. It's a good photograph of a great time I spent hiking with my wife. It's an interesting topological photograph. It was made with excellent gear. Composition is good. All of which is meaningless if it doesn't fit with who I say I am (what my interests and processes are).
Ditto this ... Nice souvenir. But does it in anyway fit an artist statement, an existing series, an interest ?
Culling is vital. As scary as it is, it feels great.
First, your remaining photographs will be excellent. Your very best and a representation of what you truly are interested in.
Secondly, it makes life simple. Just a few photographs to print, number, edit, ...
Third, it serves as a guide. As soon as you notice a pattern emerge in what survives your culling, you actively try to continue the series, explore the idea, rather than photograph passively what you encounter along the way. It makes you someone with a point of view. In other words, an artist.
Harry Potter was a monumental commercial success. When J.K. Rowling released Fantastic Beasts, the level of success wasn't the same. JKR = Harry Potter.
Imagine what would happen if Taylor Swift started to sing metal, and to do it poorly. How well would those songs stream?
Two ingredients are essential to artist brands (omitting quality, which is always, always implied): consistency and uniqueness. However flattering it might seem on the surface, being described by others as the Michael Kenna that doesn't do long exposures would be a catastrophic positioning for any photographer (me, based on the photo above, for example 😉 )You don't wan't to be compared to someone famous, you want to be your own brand.
Culling and curation will ensure only the highest quality photographs are retained and, within those, only those with a consistent style+message that position you as a unique individual. Co-author Philippe Berend is the author of those beautiful close-up portraits of decaying flowers. That is individual and unique.
One of my series is about composing in squares. Composition for composition's sake, with the subject taking a back seat. It's not a groundbreaking concept but it's mine and those who like it know what to expect from the series. It doesn't have to be rocket science, it only has to be yours.
So keep whatever photographs you want for your personal use but, for your artist work, only retain those that show a high level of quality and uniqueness. Do it for yourself, not for the audience. Remember, if no-one hates your work, you're doing it wrong!
Give yourself a zero if everything from your memory card ends up in your galleries, a low score (3/10) if you keep 10% of your photographs and a very high-score if your shoot daily with intent but only publish 5-10 new photographs a year.