I cannot know directly the mind of a terrorist,I can only infer motives and interpret actions, but the motive, I believe, contains a desire to rule by terror. The strategy is to make the victim population submit out of fear. The terrorist wants to be seen as so determined to win that nothing will stop him/her, and the victim population will have to realize that even if one terrorist dies others will step into his shoes. Those who argue for appeasement on the grounds that challenging evildoers only makes them worse are party to this strategy, for the assumptions underlying their arguments are that the evildoers have the determination that we don't. This is the coward's response.
There is another motive behind some forms of terrorism, and this is that if the terrorist organizations launch world wide attacks and are ready to slaughter millions in the cause in the end only the supporters of the terrorist cause will be left. As the Islamic fundamentalists believe that they go to Heaven while their victims end in Hell, they can afford to die in combat. So they believe that this fact empowers their success.
But did the terrorist succeed? London went about its daily business, unintimidated. Parliament met next day and publicly defied the murderer and his cause. The population gathered together in services to honour the fallen and the injured. Instead of driving a wedge between Muslims and wider British society the Muslim mayor of London led the people in their grieving. Faiths united in condemnation of the assault. No Muslim has as far as I know been attacked by angry mobs or individuals.
The dead so far included two Britons [the police officer and the elderly man] a Spanish lecturer and an American tourist, whose wife is among the injured. There was a Romanian woman catapulted into the Thames by the vehicle's impact, but she was rescued, though badly injured. A party of French school pupils were slightly injured. Rather than drive a wedge between nations, those countries whose nationals were injured stood united behind the UK. President Trump, not a man to be intimidated, gave his support, as did the French President, and many other nations. The terrorist has failed, as he has united what he aspired to divide, aroused resistance and sympathy rather than craven submission. Black people, Whites,Asians, Americans, French, Spanish and many others gave their support. There was, we could see on the news, a wonderful spirit in London, quiet but loving and caring, united and defiant against those who would destroy it. Killer, you have lost!