During the past weekend's Nymphing Master Class we had an interesting discussion.

I asked the participants on what line breaking strain they where fishing.
The replies where between 6 and 10 pounds.
And they fished so heavy because they loose a lot of fish was the reason.

We discussed this a little bit, using the 10 pound as an example.

If you fish with 10 pounds and use a bad knot, it will reduce the breaking strain by up to 50%, then you might as well fish with a 5 pound breaking strain and tie a good knot.
If you use old mono, the breaking strain reduces with sun, age, etc.
If you use a 10 pound line, you need to fish much heavier/bigger/bulkier nymphs. which will reduce your effectiveness.
Thicker line is easier for the fish to spot, thus rejecting the fly.
Or you are using a good knot, but it is not suited to a specific type of mono i.e. softer or firmer etc.

The same principle applies to a 8 or 6 pound breaking strain line.
You could be fishing with a 6 pound breaking strain, but effectively fishing with only a 4 pound line.
How good is your knots, do you check your line on a regular basis for nicks, bumps etc near the flies?

Maybe you should change your knots that you are using? Or change the brand of mono as some have a better knot strenght than others for a specific knot.