When my eye doctor told me I needed bifocals, I knew that the line would drive me crazy, and that’s why I chose progressives. I did know that the top of the lens is designed for far away, and the bottom for closeups. I presume that’s what messed up so many posters regarding stairs, but I was mentally prepared for that.
Here’s the part I was NOT prepared for. Before I went to bifocals, my eyeglasses did a wonderful job of keeping everything perfectly focused. It never mattered what part of the lens I was looking through, or even how far it was from my eyes. In fact, I could take the glasses off my head, hold them a foot away, even upside down or reversed, and everything was still sharply in focus (though reduced in size).
I was never able to figure out how the lenses worked so magically, because my understanding of the physics is that the shape of the eyeglass lens is designed to focus the image on a particular part of the eyeball lens. And yet, it always focused fine.
But when I got my progressives, if I would look in any direction other than dead straight ahead, the image was slightly fuzzy. Good enough for almost any practical purpose, but less perfect than I was used to. And being a very precision-oriented person, I was very upset.
Several posters have mentioned a “sweet spot”, and it seems that mine was “straight ahead”. If I had known this sort of thing in advance, I would not have been so disappointed, I’m glad they are teaching people to expect it nowadays.