On the ascent to Sky Pond in Rocky Mountain National Park the trail is marked with many of these cairns, as the path is indistinguishable on the face of the rock. After climbing the waterfall and passing Lake of Glass, hikers continue to climb through rocky terrain, following only these small piles of rocks.
And believe me, if you miss one, you can wander around for a while with no lake in sight.
Kind of like life. Without cairns, or guidance, we end up lost. Searching for the prize while walking in the opposite direction, wondering all the while where it was we went wrong.