Different people have different reactions to being tasered. I have a pal who is in the police and have heard many stories from him over the years.
The effectiveness of the taser depends on many things, for instance if the subject is obese or if the spread between the probes is quite small then the taser can cause only localised pain as opposed to full temporary paralysis. Also if the probes do not properly penetrate the skin then the electrical circuit doesn't complete and there is little effect. Also when somebody has high adrenaline levels it can lessen the impact of the taser. Same goes for people who are severely intoxicated.
Something worth noting is that the initial incapacitation from being tasered only lasts around 5 seconds, that is why the police move in so quickly to cuff somebody after tasering them.
In this instance there was a scumbag who had just attempted to murder two innocent people in the street and then failed to heed the police warnings to stop, continuing to come at them. That scumbag then refused to drop the weapon they were holding several seconds after being tasered despite clearly being told to many times. The person was clearly resisting dropping the weapon that they had already used to attempt to murder two people. In my book the police were absolutely right to use whatever force necessary to get the suspect to drop the knife, especially as they had both discharged their tasers so were then far more vulnerable to the suspect as he recovered further from the initial tasering.
