It seems he noticed that there was a robbery taking place in a shop in Salford and so all he did was hold the door closed to prevent the robber escaping. He was then joined by another elderly gent and together they barricaded the baddie inside. Simple. Not much skill or effort required. Not even a huge amount of strength. Simply the ability to notice an opportunity to make a difference AND THEN ACT ON IT.
Maybe there are too many people who never see the chance to do something but I suspect there are more that see the opening and then ignore it. Or are scared to get involved. Or as in the bystander effect, assume someone else will do something.
I was reading recently about the murder of Kitty Genovese in 1964 when lots of people saw it happening and no-one did anything. Since then there has been lots of experimentation on how people react to situations when they are alone, versus being with others. Everyone can see smoke and has the intelligence to think 'no smoke without fire' but will be paralysed into inaction by other people in the room. On their own they all do something.
It seems that most folk check out other people's reactions to gauge the seriousness of a situation; 'If others appear unmoved then it can't be that serious, right?'
If they are alone though they will assess how deserving a victim is for their help as well as their ability to provide it. From there they will go on to consider what assistance to provide, directly or just by phoning the emergency services and then implement it.
But for a lot of people the noticing is the issue because in groups we all tend to keep our attention to ourselves and so never notice what's happening. We need to be more aware of our surroundings, in order to observe the openings for action but also for the benefits it provides for us (see all the abundance of current chat about mindfulness).
Maybe then we will start holding more doors shut.