One of the reasons why I started with all different breeds for my original 8 chicks was because I was afraid I wouldn't be able to tell them apart.
However, now that I'm hatching incubated eggs, I often get several of the same breed, and it does take some close observation to tell some of them apart. Frick & Frack, for instance, are both bantam mottled Cochin roosters, so I gave them their similar names (because of their behavior, too), so I would say, "Frick - or Frack" when I spoke to or about them. But I can tell them apart now. Frick has more gold feathers on his back than Frack.
I have some young White Leghorns I've been trying to observe closely so I can name them individually.