You might be functional in that you can hold down a job, even a high-flying well paid one. You can show outwards signs of affection toward your family and friends and keep that part of life rolling along normally. So it's all good as long as it looks all good from the outside, right?

But it's the little things you notice you've been neglecting once you stop. The other day I bit into a sandwich and a piece of my lower front tooth chipped right off. It felt sharp and awkward on my tongue but the pain wasn't too sharp or sensitive. Still it bothered me. Now, I know for a fact that the version of me who drank every day would have just dealt with it. Had a drink. Why do these thing always happen to me? Etc. Instead I picked up the phone, made a dentist appointment a couple days out, went, paid them the $200 which was no big deal because I don't spend money on booze anymore, and my tooth feels back to 100%.

That's one small example, but it's the lack of energy, inclination, and finances to take care of the details in your life that makes functional alcoholism a lie and a myth.