What is the origin of the idiom "if it is the last thing someone do" and when to use it?

The idiom "if it is the last thing someone do" likely stems from the idea that when someone considers a list of actions or possibilities, the one mentioned as "the last thing" is the least preferred or the least likely to be chosen. It is commonly used to convey the depth of their commitment and highlights their readiness to go to great lengths, portraying a strong resolve that surpasses all else.