An analogy:-

Let’s imagine that you are about to enter your bank, the First Bank of Commerce, to transact some business, when you notice there is an old man standing outside it, holding a placard upon which is printed the words: “This bank robbed me.”

You wonder what is going on. You have always found this bank honest and above reproach in all of your dealings with it. As you approach the man he thrusts a leaflet in your hand.

He shouts at you “Hey, Mister! Don’t go in there That bank will rob you! All banks are nothing but evil robbers, crooks and shysters!”

You are intrigued by him, so you decided to stop and ask him what his problem with the bank might be. “I notice your placard says that this bank robbed you. When was that?”

He says: “All banks rob you. Why, I put my money in a bank just like this one and they robbed me! Take my advice young man, do what I do. Don’t put your trust in the arm or the strongbox of a banker! Look to yourself for your own security! Keep your money under your mattress!”

You notice that the man had failed to answer your question. “I am sorry to hear about your problem. But sir, when did this bank rob you?”

“All banks are exactly the same. It wasn’t this bank that robbed me. It was the Bank of Smith that robbed me. But all banks are the same, I tell you! They all rob people!”

You are slightly irritated by him, now. After all, he hasn'ty been truthful with you. His placard boldly stated that the bank he was protesting against had robbed him, but now it seems that he was not telling the entire truth. It had been another bank that he had had a problem with, not this bank.

You try to reason with him. “But sir, surely you cannot extrapolate from your experience and declare all banks to be, what was it you said? Oh yes! ‘evil robbers, crook and shysters’? I am sure some banks, perhaps the majority, even, are honest in their dealings with their customers?”

At this, he becomes enraged! He starts screaming at you: “How dare you question me! If I say all banks are robbers, than they ARE, robbers, damn you! What are you? Some kind of pro-banking nut? It’s bigots like you who allow bankers to rob the people! Use a mattress to store your money! It’s the only way. Or maybe you are a spy from the banks, trying to shut me up?”

You angrily sidestep this ranting man and walk into the bank, wondering at how anyone could unjustly extrapolate such a specious argument? After all, there were commercial banks, bank, building societies, community banks, savings clubs, and the like. How could he condemn all banks based on his experience with only one of them?