Most of the time, it isn’t your technique. Paint straight from the tube doesn’t have enough binder relative to pigment to level itself once it’s on the canvas, especially with stiffer colors, so brushstrokes drag and the surface dries uneven instead of smooth. A small amount of the right medium fixes that. Too much causes its own problem, longer drying time, a glassy look that loses texture, so the goal isn’t more, it’s just enough.