And it is more likely that an experienced brewer, like myself, will slip up in our process/sanitation practice, or have scratched equiptment/gunk hiding in our hoses from lots of use, or from just becoming overconfident/ lazy, then a hyper vigilent, first time or beginning brewer using the most rudimentary of sanitization practices on relatively new equipment.
But for all that, beer is a lot hardier than we give it credit.
Some people come down on me for saying this, but beer has been made (nearly spontaneously) since the Ancient Babylonians, and up until Louis Pasteur came along, with almost no knowledge about sanitzation practices.
And yes it may not have tasted as good as ours today (or maybe it did, we'll never really know), and yes sometimes it got infected BUT it must have been uninfected most of the time, and must have been damn good or else we wouldn't be drinking it today...it would have gone the way of the betamax, or Pepsi Clear, or New Coke, if most of the time it sucked.
So even the sloppiest of our sanitation practices blow away the ancient methods...even us simply having an enclosed place, clean fresh water, and the fact that we bathe on occasion is more than the ancients had...