Each movement (when free handing) that we do offers a chance to slip or do less than precise movements that add up to a larger mess.
When free handing, most of us are kind of sloppy to start with and because of the lack of muscle memory obtained we're slipping and going from about 5 deg to 25 deg on each stroke. Sounds crazy but not that untrue.
Since many people start with something similar to King 1k (most unfortunately often recommended first stone) as a starter stone then we find ourselves making facets more than we're cutting a new crisp bevel. Our bevels look like a whole bunch of multi-facets vs a clean single facet - this is because we wobble and our stone doesn't cut fast enough. If we stop here at 1k though we might get lucky and still have a coarse enough edge (even if multi-faceted and somewhat rounded) to grab and cut food.
Should we continue to a finer grit stone then we'll be polishing the multi-faceted edge taking out the bite left from the coarser stone and now the knife won't cut much of anything.
But this isn't ever good enough for us so we get out the polishing stones to fix this and guess what we do? We make the edge even more slick and rounded.
The more stones we use the more we wobble and the higher the grit stones we use the more we polish and round the edge.
I recommend making sure that the first stone used in the series is coarse enough to cut faster than you can make a mess of the edge (from wobbling) and then to only use enough stones to go from this point to get the edge to where you want it. The fewer stones used the better and this is why getting stones that work together, allowing large jumps in grit size, is key.
Also worth noting is that you want to spend as little time as possible on each stone for all the above reasons and again getting stones that work together helps keep you from screwing things up.
Here's my tips to success...
1. Use a coarse enough stone as your first stone to allow cutting of a clean crisp single facet bevel. The stone should cut fast enough to keep your wobble from screwing up and creating the dreaded multi-faceted edge.
2. Use stones that allow big jumps to where you're looking to go to. If you can jump from 400/500x to 3k then yeah that's great.
3. Use as few stones as possible - less time on stones equals less wobble. using stones that (again) allow for this helps a lot.
4. Go no higher than 5k(ish) for double bevels. Singles are different - go as high as you like - maybe the deba would be best left at 3-5k though.