I am by nature a more academic painter in the studio so field sketching can be a great departure for me. My approach to sketching is to allow myself the freedom to discover the image and explore the medium, keep to the fundamentals and just observe and experiment.
I often wonder about the percent of paintings that work out.
But in reality all studies are successful if there is at least one thing learned or idea born from them. I think as you get some time and distance from your sketches you can see their qualities with fresh eyes.
I like the starts better than the more resolved sketches. They leave a bit to the imagination but still carry a sense of place. When it comes to sketching on location I think its better to have many good starts then to keep plowing along on a little canvas trying to get it to work for you.
The adage is that if you want to be good at anything you have to work at it. An artist can work all day, cover miles of canvas, and accomplish absolutely nothing; an artist must be dedicated to growth, the journey of invention and discovery.
That is what gives you confidence.
I like the definition from Wikipedia for oil sketch.
All are oil on panel, 8x10 with the last sketch 5x7.