I promised you an invisible increase. Now that you’ve learned the KRL (knit right loop), you’re ready for it.
With the KRL you knit into the top loop of the stitch immediately below the stitch on your left needle.
The invisible increase begins by finding that same top loop of the stitch below the stitch on your left needle, but from behind.
Turn your left needle a little to make this top loop of the stitch below the stitch on your left needle easier to locate.
Bring your right needle into that loop from the top down. Knit into that loop.
But wait: if we were to bring that knitted loop up to the right needle at this point, the way we did the KRL, we’d still see a tiny hole. So instead of bringing the knitted loop straight up to the right needle, we place it on the left needle and knit into it again.
We can consider this a lifted stitch that’s been reknitted.
Now it’s a keeper. And an invisible one, at that.