Thinking in terms of the choice to stay with the 99 or go after the one lost sheep, and assuming that most would make that choice whether sooner or later, the decision to go after the lost sheep is most likely influenced by the degree of safety involved in the perspective situations, and the lone sheep would be in one of a more immediate risk of danger of harm. The 99 are in an open field which means that, although they are vulnerable to harm if left without the shepherd, he can still keep a watchful eye on them knowing where they are whereas the one sheep is lost so its whereabouts are unknown. Additionally, I assume it would be contingent upon the shepherd finding the sheep that he would have to leave the 99 in order to focus on hearing the single lamb's bleating.
The female valued of 10 shekels angle is interesting, but I don't think even a single coin of silver was considered trivial enough to leave lost, like we might let a nickel, dime, or penny roll under the counter without exerting much effort to retrieve it. However, if a silver ounce, I don't know how much they're worth these days, as much as $25 or maybe only $17, fell down the sink drain, who among us would immediately rummage through the toolbox for a wrench?
