Notes On the Fly
When you begin to really 'match the hatch' try to catch a few of the bugs and really compare them to your imitations. My tying and fly selection really began to change when I started this process.
Your perception of a bug can be a little different than you think when they are in the air, on the water, or even in your hand. I know after a few years of matching the hatch successfully I still struggle with this same thing!
I picked this fly (seen in the image above) a #20 Medallion Trico Dun because it appeared to be the correct match when I first examined the air and water. Not until I caught a bug and tossed it in my trico box did I see I was 2 sizes off... as usual I needed a smaller pattern. Right around the time I started putting real bugs in my fly boxes was when I started tying all my flies smaller... and catching more fish. Give it try and see if it helps you.