People do love to try and define our personalities by our behavioral habits and physical features. Some are based in science, others on simple studies on a sample of people and others may just be a personal theory. I found this theory which correlates your nail shape to your personality. I’ll let you decide how accurate it is.
When thinking about what you can tell from the shape of your nails, if they are longer than average, it means you’ve shown them enough care and attention to allow them to get to that state in the first place! People with longer natural nails are likely to be attentive, generally well mannered and respectful of other people.