Over-Sharpening

[SteveG]

I've read a couple of times that continuing to sharpen past a certain optimal point reduces the sharpness of a blade.  This isn't something I've experienced with plane-blades or chisels, and my knife-sharpening skills are poor enough that I wouldn't notice (unless I measured a lot more often than I do).  Anyhow, it doesn't make sense to me, so I'm hoping somebody can explain why that would happen.  I can understand it if the sharpening is with a soft substrate, such as leather stropping, then it would make sense (and dubbing a perfectly good edge is something I've done all too often).  But I don't understand how/why it would happen with stones, unless it's simply due to burr formation.  I'm not disputing the claim, I simply don't understand the how/why.  If anyone has an explanation I'd love to hear it, and if it's something other than burr-formation, I've very, very curious, indeed.