We are all familiar with "chain reactions". These occur when one action creates another action which creates another and so on. It can be as innocent, using the term lightly, as my son sliding his plate across the table which bumps his brother's glass of milk, which tips over, spilling said milk on said brother, which results in the brother erupting in tears and anger, which results in punishment for both brothers, which results in an evening of writing lines and washing clothes. All of this because of simply sliding a plate across the table.
Chain reactions are not merely confined to the physical world but also exist in the spiritual world as well. It can be as innocent, again, using the term lightly, as neglecting a regular prayer life, which in turn weakens a resolve against sin, which gives way to entertaining the near occasions of sin, which in turn gives way to actual sin, which causes self-hate, which causes despair, which causes more sin, and on, and on.
However, chain reactions need not always be negative. Good chain reactions can come from good actions. This is the idea behind the popular "random acts of kindness" movement. These acts have the consequence of causing other good things to happen. A man anonymously pays for a fellow diner's lunch, she in turn leaves a large tip, the waitress is now able to pay for the medicine her mother needs, and on, and on.
The difficulty with good chain reactions is that unlike the pushed plate, spilled milk, and events that follow, we aren't always able to see how our good works affect others down the line. The anonymous patron will have no idea that his gesture helped save the life of the waitress' mother, the woman who watches the waitress' son, who will one day develop a life-saving procedure for stroke victims.
In the spiritual life, positive chain reactions are also difficult, if not impossible to see. We can't see the effect that our prayers have on the lives of others. We can't see how our daily sacrifices have helped bring someone back to the Faith. Yet, this in no way should deter us from doing such things. If it does, we need to run to Confession because we are doing these things out of pride. No, we may not see the fruits of our labor here on earth but we will in Heaven. One day, when all is revealed, we will see the great chain-reaction of our life and how we affected others - for bad and for good.