I will start this off with a short story. My younger sister Jennifer is responsible for this simple way of explaining the ladder or invisible stitch. At the time she was 6 and learning to sew under big sister’s (me) tutelage. Keep in mind that I, up to this point even had trouble with the stitch that our mom had tried multiple times to teach me. It was Jennifer who managed to understand it and then simplify it.
I’ll explain it as my sister did to her first grade class many years ago as it was a *very good* way to explain it (Don’t take that as an insult it’s just how old she was when we taught her to sew and how quick she picked up how to do things and how she simplified it so that her peers could understand!)
She said to imagine the two folded edges of your project as river banks with the space in between as a river. Your stitches need to follow the river’s edge (fabric fold) and then make a straight bridge across the river (space between), travel along the opposite bank (inside the fold of the fabric) and make another bridge back to the other side, repeating this all the way down the river (space you are closing up). Every few stitches (2-3) you pull and make the bridges pull the river together. At age 6 this was a good analogy and worked to teach her first grade and second grad classes how to sew.
My mom was a camera nut and helped during that day in the classroom and got this on tape so I got to see a replay of it after I got home from school. At the time I was the one teaching her to sew. My sister is now 26 and sews in half-inch scale. Below is a diagram from one of my other patterns that illustrates to help with visualization.