There is a good hatch of aquatic insects on the stream and the trout are feeding well upon them. You catch several of these insects and by carefully selecting a dry fly from your box you are confident you have a good match for it. However, fishing this fly to rising trout for half and hour does not bring a single strike. On each of your presentation casts you can clearly distinguish your fly from the naturals around it. Then it dawns on you…if it does not look exactly like the naturals to you, it probably does not look like a natural to the trout. Most likely your fly is too large or the wrong color…Try again.