Vaccination - an Analogy
Vaccinations are effective at creating mutants. No, that doesn't mean that your children, or children's children (if you were so lucky), will be born with three eyes or the ability to spit flames out of their ears. Let's face it; if that were the case more people would be doing it. Here's a stab at an analogy that might be clearer than the paragraphs of genetic jargon that most don't bother trying to understand.
Imagine your body is a little fort set on a grassy plain, fairly stable and feeling as secure as it is possible to be. Sure you have all the little subsections of it with their own little jobs, but concentrate on the relevance of your many little soldiers (purely in the metaphorical vein, notthose other "little soldiers") as they constantly patrol about your fort. No real problem arise since your troops get the attention they need and replaced as the need arises, a somewhat grave assumption/generalization really, but just pretend. Suddenly, one day a band of merry barbarians ransack another fort nearby (or so you've heard from your friendly high-ranking forts). That battle was messy, with the civilians shaken and many soldiers lying splattered or little more than mush spread along the grassy knolls, but the barbarians were driven off, or even wiped out. It sounds quite terrible but for the purpose of this example this is natural; a brief cleaning job and a little while to recover, more than likely calling in some outside support to rebuild, and the only remnants of the fight would have been a tactic developed for future reference. Completely normal, it happens all the time, sometimes the troops are the only ones to even realize anything is going on.
But you're not like those other forts that let their soldiers get splattered everywhere, maybe you don't entirely trust these outside reinforcements that are offered as an easy, if daily part of routine. So you look around and find out that the larger, high-up forts are offering this way that assures that after a little pinch you'll never have to worry about having to put your little soldiers in jeopardy. Oh, it seems too good to be, but you trust these big people to take care of you. They've taken good care of you so far, haven't they? They set up your transports efficiently, paved secure trading routes and made sure you had a comfortable existence, right? Oh, I'm sure they're getting on that soon then. Regardless you trust they have whatever you need since they're on top, even though you didn't vote for them to begin with, and so get set to have this miracle reinforcement.
Soon after you receive a small box at your doorstep with no instructions, but your troops know what to do. You have a handful of those fearsome barbarians, or at least you assume they once were, tied to polls desperately trying to reach at their dulled swords while their nasty upbringing is the only thing still keeping them up. The rest of the afternoon is a lovely time bashing at the gimped barbarians with flails while others examine the technology of their not-at-all-useful weaponry. This was a productive day; surely you've raised morale, prepared yourself for the enemy's offensive capabilities and even found the best places to aim at. Immediately you begin fortifying your walls; no more of this wood stuff, brick and mortar that no pike could penetrate. Why, you're impervious! Those barbarians take one look at the thick, tall walls that are your defences and turn away to look for someone else to annoy, but alas, everyone else in range of their mules has already done the same as yourself. Surely they are now a dying kind, and you did your part to survive.
A month later the barbarians return to your doorstep in the hundreds, toting full plate armour, catapults, trebuchets and other siege engines. You weren't expecting that, I'm sure, but the barbarians learned from their neighbour's mistakes and came prepared. How did they do it? Well, they're not as stupid as one would make them out to be. They waited, they grew in strength and number after some reports from what survived in past attacks that were successful. But you were never attacked before! Right? How could they know your defences when you've never actually met (that you know of)? Oh wait, you got that little crate some time ago, which thousands of others received as well, exact copies in fact, and these new and improved super barbarians don't need to know what you can do since you prepared the exact same way as everyone else. Now the higher-ups ask you to get this other little parcel that will hold off an invasion, and you trust them because you didn't have much trouble after the first time.
So what about these people who went crazy and refused the package of gimped barbarians, and took these reinforcements on a regular basis that you shunned due to mistrust? Their forces are large and resources vast with stores of equipment and provisions for battle. They prepared for everything, even if their defences don't seem to be substantial to you. Their forces can continue to fight longer before dwindling, though that is of little concern as they increase their reinforcements daily. They can deal with the average troupe of barbarians as if it was hardly a nuisance, and they can even stave off the oddities that you helped create. There are more of them, significantly, and they operate much faster with their surroundings, heavy plate and siege weapons be damned.
What relevance does this have to anything at all? If you have to ask, then you've missed the point entirely. Go to your mailbox; you probably have a package waiting.