How many times is it acceptable to be fired?

Next was years later and technically a 'comprimise agreement' in that I was obviously not up to the job six months in, they said here's 12K to fuck off quietly. Sad at the time though.

Don't understand why they would give you a compromise agreement if you were only six months in. I've had experience of these too but only where ive been employed for well over a year. Some kind of Union job or banking?