As I reported earlier, I missed an interview with an international employer because AA, though aware the flight was not going to arrive on time, said NADA about that fact, thereby preventing me from informing the interview team of my enforced delay.
Yes, this occurred before the days of cellphones and ubiquitous internet access, back in the seventeenth century, as it now seems.
And so, especially angered by their repeated, canned, "oh fly with us amd give us another chance" reply letters (what, another chance to mess up my schedule again?) as a UA1K I've never given AA my bux for lo! these several centuries.
From what I learn here on FT, though, writing the "I'll never fly" letter just lets the offending off the hook; if they think I'd never spend money with them again, they're hardly motivated to work to earn my business or compensate me.
Ironically, a UA RCC concierge put me on the last/only available flight out of MCO during weather problems some time ago, a dreadful AA 767. BleAAgh!