What's a primary difference between the experienced triathlete and the newbie? A keen and highly develop sense of self-awareness. It's that intangible quality that's critical to success in long distance endurance sports events that often times makes or breaks a result.
Self awareness is trainable, just like lactate threshold. And just like training other components of fitness, developing a highly tuned sense of self awareness takes practice and patience.
Now with modern training technology, you can monitor every fitness metric and analyze it to death with sophisticated software. While this data crunching is effective (if used properly) and plays an important role in learning more about how your engine runs, it's still important to not overlook signs that your body is plainly communicating to you... signs of fatigue, over use, burn out and just plain 'blah'.
The self-aware athlete is the one who notices the twinge of discomfort in the calf while warming up for a track workout and decides to go easy with a zone 2 aerobic run workout instead, and then stretches and rolls it out post workout. She's the athlete who notices a change in appetite and increases or decreases caloric intake to meet daily energy demands from training. And on race day, she's the athlete who knows how best to 'burn through her matches' to suit the distance and difficulty of the race course and conditions.
Self awareness is a key component to success in triathlon and all endurance sports. Listen to what your body is telling you regardless of what's on your training schedule that day or showing up on your power meter. It's usually right on task.