To be good at something you have to work at it, and even then it might not be brilliant.
Portrait painting is very hard.
If I painted a thatched roof I would put the paint on thick and then use a toothpick to scratch out the thatch.
I am good at painting Sky Trees and Water.
If I paint Snow I would put an underlay of Blue first then paint over the top. Some oil paint colours are Opaque. There would be other cols in the snow like patches of sky blue and dark yellow.
I love mixing and playing with cols. I never use Black because it is dense and looks like a hole.
If something was not right I could rub the paint off with a cloth.
Turpentine or linseed Oil ...which can be bought as a medium is used to thin the paint.
Too much Turps could make the paint crack but dries quickly.
Something went wrong ... So I had to put a title in ... Perhaps I created a new topic.