The proverb is based on what various creatures are believed to have chosen at the beginning of time. The Karanga culture is rich with stories of animals with human characteristics including those set in a time when animals could talk with humans. Some of these traits include choosing some of their features and characters. In this same spirit it is believed that the tortoise is the one that chose to have shells on its back which are considered a burden by others. Hence regardless of others viewing shells as negative, it was in fact the choice of the tortoise. Our elders then drew the lesson that one cannot question the heart's desire - it is what it is!
The proverb is used to explain peculiar choices that may be made by someone and as a way to prevent further questioning by stating that it is their will and it must be respected as such. The proverb is also used to dismiss those who try to undermine someone’s choice by thinking the person should have chose differently.