Take a look at this picture. Can you see the problem with it?
Of course you can. The feather is just stuck into the skin surface. It doesn't look like it belongs there and it certainly didn't grow there. Compare that with this photo:
Once again you're looking right at the point where the feathers are glued into the skin, and you can see it looks much better. Obviously it helps having more than one feather in place, but the main reason it looks so much better is that I've wrapped a sliver of paper around the shaft of each feather and blended this little paper bump into the surrounding skin.
In this photo, the glue is not yet dry and the paper hasn't been painted to match the skin, so you can see how the technique works.
This technique works because it imitates the follicles that real feathers grow out of. It also helps to insert the feathers on a slight angle.