My motto is "set targets, not goals." If my goal for the day was something like 30 miles or 1,500ft of elevation, I'll easily go out and do 40 miles with 2,300ft and feel like I did great, because I killed both of those goals. Then I pay for it the next day. So I set a target of 30 miles-- and try as hard as I can to pull back into the driveway right when the miles tick over from 29.9 to 30.0. You don't necessarily have to limit your intensity, if you limit the duration. You just need to cut back on one or the other.
Moderation is hard-- I need as many digital nannies as possible to keep me from overdoing it. I give myself arbitrary kJ limits, max HR limits, mileage or elevation targets, etc. Keeps it interesting.
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