There were two twins on my course in college for the last two years. Not quite sure what defines twins as being truly identical but they did look really similar. I could tell them apart initially because one wore their hair different from the other, plus one of them wore glasses and the other didn't. Eventually though I noticed other differences between them like in the shapes of their faces (something you wouldn't notice initially) to tell them apart even if Lynsey wasn't wearing her glasses. I never saw why people had trouble telling those twins apart.