OK, I understand that sometimes a particular beer runs out, or the crisp flavour you fancy is out of stock. Predicting the peaks and troughs of customer demand is as much of an art as it is a science, and pubs don't always get it right.
I like to think, though, that no pub could get it so entirely wrong as the bar I was in last night - the patrons bar at the Fairfield Halls in Croydon.
It was a big night for the veteran pub rock community of South London. Not only were Jools Holland and his Rhythm & Blues Orchestra playing in the concert hall - with guest performer Dave Edmunds - but rockney legends Chas & Dave were also strutting their stuff in the smaller theatre at the same venue.
And yes, before you start sniggering, I was there to see Jools. Even so, I've no doubt that Great British Beer Festival veterans Chas & Dave put on a good show too - but thanks the excellent soundproofing, I didn't hear even a single note of 'Rabbit'.
Back to that bar, though. It seems to me that any venue anticipating the arrival of hundreds of rock fans at more or less the same time ought to be geared up to shift a few pints.
Not so. The queue at the bar 40 minutes before showtime was phenomenal. The two staff were not only unprepared to meet the demand for drinks, but also demonstrated an approach to queue management which seemed almost guaranteed to provoke a lynching.
People who had patiently queued were seeing other customers push straight to the front, with priority service apparently given to those who shouted loudest.
We eventually managed to procure a warm bottle of lager - which I mistakenly thought might be a better call than the one standard draught lager on offer - and an overpriced glass of wine, at an ancillary bar upstairs.
This was only manned by one member of staff, who again demonstrated a very limited grasp of queuing etiquette. Any attempt to order interval drinks was rebuffed with an explanation that under a new system these could only be ordered from the aforementioned main bar - downstairs and packed to the gills.
Now, I understand the problems of planning staffing levels for extended open hours. But this is a venue that knows exactly when its peak demand will occur - for around 45 minutes before the event and 20 minutes during the interval.
I can't belief that the cost of a few extra barstaff for these periods wouldn't be repaid many times over by increased sales - especially if the bar could also stock a decent product range.
It was a great gig, though, since you ask, with the sound of Dave Edmunds striking up the opening chords of 'I Hear you Knocking' still making the (now sadly grey) hairs on the back of my neck stand up.
Back in the days when Dave played in pubs, though, you could have had a decent pint as well.