I'm running my five mile loop tonight when suddenly I gain consciousness during mile four. I have no recollection of mile three. Did I run mile three? Well I'm here aren't I. But it is possible for me to cut a corner and miss part of mile three. Think; think. Panic begins to set in. Wait, I remember now. Or at least I vaguely recall struggling up the hill on mile three. Or was that yesterday? No; it was raining yesterday. I'm pretty sure that was today.
Ran five miles tonight. I think.
Use my Garmin you say? In the words of Willy Loman, "Well, yeah, but who ever thinks of turning it on?"