Coffee alone is no big deal. Neither is cable. Neither is a "normal" cell phone bill. Neither is a monthly mani-pedi. Neither is buying just a little bigger house than you need. Neither is a second kid. Neither is getting a dog. Neither is having a landscaper trim your lawn. Neither is a little nicer car for your little bit longer commute to your little bit house where your extra kid plays with the dog on your well manicured lawn...
But when you stack enough of this crap up in your budget there is nothing left (or less than zero). Many folks grow into adults like frogs in a pot, adding on as income grows. A small luxury here or there seems small in the overall budget, but pretty soon folks find themselves "needing" a wine club membership to keep up with the Jones's. Most can't see the ridiculousness of their own lives and can't figure out how anyone making a mere dual 6-figure income can manage to save anything for retirement.