I think a lot of artists of every sort work at their art or craft and along the way they become rather skilled, and get to a plateau.
This can present an obstacle to further development as an artist. One thinks of the writer of a mystery series, for example. The detective has been created along with a certain world, and if successful the writer begins to publish the mysteries. It is true that some writers can remain true to themselves and their craft in this way. Agatha Christie wrote plays as well as had several different series of mysteries with different characters, and I think achieved a lot.
In the world of the painter/artist there are again many possibilities. I can say that for a number of years I was just experimenting with different styles, materials and techniques, always trying to make something that had something deeper in it. In the past few years I have begun to do strictly painting, and this is a limited technique which draws on a lot of other things I have learned over the years. But still, there is the huge danger of reaching a plateau, with which I associate the word mediocrity.
A plateau artist is someone who has hit on a style or subject that sells, perhaps, or who has mastered a certain technique so that painting is "easy." I sort of think that when it is too easy your eyes have blinders. We need to go back to the great poet Basho who traveled and distilled his experience in the most intense Haiku.
There are so many approaches to the start of a work of art, and then for me, there is the destroying and starting again. A piece that turns out to be successful must have a surprise in it, not only for the viewer but for the artist who made it. And that surprise isn't just some arrogant flip of the brush, but the result of letting it sink in and trusting to one's own inner being but at the same time being open to everything in pure mindfulness.