Ditch Your Garmin
Pace vs. Intensity. Do you know the difference? There is a difference between pace and intensity, with intensity being much more important for runners due to the myriad of factors that can affect the pace. Trying to hold yourself to a given (numerical) pace without accounting for temperature, humidity, terrain, wind, hydration/ fueling status, energy levels, clothing selection (ability to sweat), and race experience may do you more harm than good in a race.
It's very possible that holding yourself to a given intensity will bring you to your predicted- or goal-pace (or vice versa), but always consider the race conditions (course + weather) and your body's real-time status first. This may sound like common sense, but then why is it that Garmin runners are less likely to be at peace with their finish time? Answer: Their craving for data is too strong.
The same personality trait that wants to buy the Garmin in the first place is the same personality that is going to overanalyze the data mid-race (key word). Obviously, this does not describe all runners in this category, but in my experience as a coach, a Garmin watch ends up serving only 1 purpose for a runner: It tells them they are slow and/or could have run faster, either of which leads to a dose (great or small) of feeling unsuccessful. As much as a runner wearing a Garmin may tell you, "oh, it's a hilly course, I'll just run based on feel," I bet you dollars to gel packs that he/she will forget all about that idea once the gun goes off and when they take that first peek down at their watch, and mutter, "boy, I'm way slower than my PR." Talk to that same runner after the race and you'll hear, "well, it was a hilly course, I ran pretty slow, not a good race for me." Aren't the hills supposed to affect your pace? Yes. So then why would the runner use the phrase, "pretty slow" and "not a good race"?
Again, I offer that it's the personality of the runner that adores data and numbers; therefore, faster pace (faster numbers) are more attractive to look at and are typically dominate this runner's thoughts mid-race. In turn, this data analysis creates an unlikelihood to accept the slower paces that are predictable based on race conditions (terrain + weather). Ultimately, the runner feels slow, or is less likely to feel successful. I see this distinction all the time between the runners I coach who use a Garmin vs. runners I coach who have a simpler watch using only elapsed minutes and seconds. Having stated the above, you can imagine how much worse it gets when the Garmin signal cut out and "throws off their pacing."
Bottom line? Race based on intensity (perceived exertion). Garmin watches (and heart rate monitors) will not always guide you when you want to actually race someone. Knowing how your body is reacting in real-time is more important than the actual pace you are holding. For instance, being very in-tune to your rhythmic breathing and stride length during training will enable you to know whether or not your effort can be sustained during a race. I would like to see more runners ditch their Garmin completely, and I'm successful half the time. If that doesn't happen and you're still going to race with one, then my final reminder is that a Garmin should not be telling you how fast to run during the middle of a race, it should merely be satisfying your curiosity.
The pace is merely a byproduct of the course conditions and shouldn't dominate your thoughts. Proper pacing is related to the phrase "staying in your element." Your element is your stride length, cadence, posture, amount of tension in your body, the nature of your thoughts (positive vs. negative), and your breathing, which are all of the things we hopefully tune-in to occasionally during training.