Let's start by defining "easy." For me, "easy" is not about how quickly words come to me. "Easy" is if the movie playing in my head flows smoothly, clearly, and in great detail. Great detail. I need to see the dust motes in the moonbeam and hear the white noise from the speakers set six feet apart in the acoustic-tiled ceiling. I need to know if that funk in the air is from mold, cold tobacco ash, or a broken perfume bottle. Is that creaking from leather or a tree branch? The level of detail that goes beyond the conversations and broad-stroke setting. The mood. The small actions the characters perform. I need all that excessive detail to feel immersed in the scene.
Total immersion is critical...and so is total control.
How many times can I rewind, pause, and play that exact scene without losing clarity or changing anything? The more I can do it, the more I can live and relive each moment while the camera pans left, right, and 360, the more I exist in the scene.
All that is what makes writing a scene "easy" for me.
Now, of all the scenes I've written, which scene was the easiest? The one before the one I just wrote, of course!