Often people comment on the size of some DSLR bodies such as the D7100 or D600 and recommend a grip to resolve the problem, if it presents one.
I then go and look at my old Pentax ME Super and Nikon 601 and the are small by comparison. How did people manage to hold these older film cameras?
Note the attached 'tube vid and fast forward to mark 9:28 where professional photographer Mike Drew and Chris Niccolls are discussing the feel of the Canon 5D MIII vs the Nikon D800. At about mark 9:48 Chris Niccolls jokingly says he has "tiny girl like hands which are fantastic for . . . I don't know . . . picking locks and knitting . . . embroidery. . .” so the D800 feels great to him, whereas Mike Drew has larger hands and says the Canon 5D MIII feels great to him.
After owning a D7100 about 9 months (and dropping it at a cost of over $300 for repair), and then holding a Canon 5D MIII, I have to agree with Mike Drew. With my
polar bear hands the Canon 5D MIII gives me greater confidence then my d7100. I even considered selling it to buy a 5D MIII, but after comparing the brands IMHO Nikon has more pluses going for it. My solution for the time being was to buy a grip.
I've been told the D800 hand hold position is slightly larger. Maybe like Chris Niccolls, your hands are smaller. There's no way for me to know your situation but these could be reasons why it's difficult for you to grasp how others may feel about the D7100 grip.