Even Pret a Manger does not get it right every time.
I call in every morning for coffee and porridge and although it is spot-on 95% of the time I do occasionally get to work to find that they have given me the wrong coffee, or the wrong topping on my porridge - and even, on one occasion, insufficient change. The service depends very much upon the store you go to - the branch across the road from my office is superb, whereas the service in the one around the corner leaves a great deal to be desired.
No-one gets it right every time but, to bring this back on topic, in all my years of travelling BA has been one of the most consistent of all airlines in delivering a good product. I have had such dreadful experiences with Lufthansa, Air France and SAS that I will not use them again, whereas my sub-optimal experiences on BA have been rare (and resolved quickly and courteously when they do happen). As a result, BA is still the website I go to first when I want to plan a journey.