In introductory category theory books, it is often given the example that given a preordered set, we can obtain a thin category from it in the obvious way. Sometimes they go as far as to say that preorders and (small) thin categories are the same thing. This is perhaps forgivable because at that point the notion of equivalence of categories isn't defined yet and/or they mean (small) strict thin categories instead. But it still makes me wonder to what relation is there between the usual category of preorders and the 2-category of (pre)orders. The latter is equivalent to the 2-category of partial orders so it seems to have less information. Is there some natural way of obtaining the usual 1-category of preorders from the 2-category of partial orders or from the 1-category of partial orders without breaking the principle of equivalence? Should we really be thinking of thin categories as partial orders as opposed to preorders?
For extra motivation, some other wrong example that is often given in introductory category books is that they say groups are the same thing as groupoids with exactly one object. However we can recover the usual 1-category of groups from the 2-category of connected groupoids: we do this by considering pointed connected groupoids. I was hoping/wondering if something similar can be done to recover preorders from thin categories.