The most obvious answer of course is when results are so bad that there is no other option.
It’s an intriguing question and there have, during my time as a sports journalist, been many times when I would have loved to have been a fly-on-the-wall in a chairman’s office to see what reasons were given and how the process was carried out.
But the question came into my head mainly because of what has been going on at my club Norwich City in recent weeks.
We find ourselves heading into a weekend where it has become pretty obvious that Chris Hughton is in a situation which will see him given the boot if the Canaries fail to beat Hull City at Carrow Road.
Certainly that was the feeling I got as I read the quotes from chief executive David McNally in which he failed to give Hughton his long-term backing.
Ultimately, football is a results business and if results aren’t forthcoming, it is the manager who pays the price. You can argue that the players should take their share of the blame, indeed they should. But, rightly or wrongly, that isn’t the way football works.
Those of you who follow me on Twitter will know that I have been fairly outspoken about Hughton.
Clearly, he is regarded as one of the good guys in football. But the truth is, after the high standards set by Paul Lambert, Hughton has failed to deliver for the Canaries. One look at Norwich’s record in 2013 would suggest he is still fortunate to be in with one more chance of holding on to his job.
I made my mind up after City caved in when being beaten 7-0 at Manchester City. And that thought process has only increased with time, not least on Tuesday night when a pitiful display against Fulham’s reserves ended the interest in the FA Cup.
There is a lot on the line in the Premier League these days and the Norwich hierarchy have made it clear that staying up is the only option, that is the sort of talk that makes results the only thing that counts.
But while I do believe that Hughton should go, I now wonder whether this is the right time.
Had he gone after that game at Manchester City, it would have given a new manager plenty of time and a full transfer window to play with.
Right now, there is less than half a season to go. Is there another manager out there who could change the fortunes around quickly enough? Will he be given the chance to spend in the next couple of weeks? How would it look if Hughton was sacked and we went down?
All questions that must be running through those at the top of the club. I don’t envy them.
The situation can be brought closer to home in these parts.
Whether he was actually sacked or not, we will never know, but Chris Plummer left Corby Town after only the second game of this season as a 3-0 home defeat to Burnham was followed by a 6-0 thrashing at Hemel Hempstead Town.
Was it the right time for him to go? Probably, he had after all overseen the Steelmen’s relegation from the Conference North in April after they had looked safe at Easter.
Has his departure been for the good? In general, the answer is probably yes. Andrew Wilson and Tommy Wright led Corby on a decent FA Cup run and their season isn’t over by any stretch as they look to launch an ambitious burst for the Calor League Premier Division play-off places.
On the other side of the coin, there were plenty of Kettering Town fans who were calling for Dean Thomas to be given the boot after they suffered five defeats (some heavy) in their first seven matches in the Calor League Division One Central.
But chairman Ritchie Jeune held his nerve and backed his manager to turn things around.
It has taken a big overhaul in players but that stance from Jeune has been proven to be the right one. No-one needs reminding that Kettering are unbeaten in 14 matches and in contention for the play-offs as they head into the huge clash with second-placed Rugby Town tomorrow.
It seems like it is all about timing when these big decisions have to be made.
I fear Mr Hughton’s time might just run out this weekend...