Reasonably, resistances are built not only through our use of antibiotics but because these microbes are in competition for resources. Mold, viruses and bacteria are often comfortable in the same environments and want to keep all of the resources available to themselves. It is natural that some of these bugs will build natural tolerances to the defenses of their natural enemies that have built defenses to kill them.
https://www.nature.com/articles/ncomms13803
Additionally, every time someone washes their hands in the hospital, some of these bugs that get knocked off and survive hang out in the drain pipe and party with other bugs and in doing so they trade gossip: such as how to be resistant to certain defenses of common microbial enemies. This happens through genetic swapping between them.
http://emerald.tufts.edu/med/apua/about_issue/about_antibioticres.shtml
We certainly exacerbate the issue by swallowing pills every time we sniffle and mostly do more harm to the beneficial microbes in our gut and on our bodies by doing so. The building of resistance to antibiotics is a natural progression of the microbial evolution. Its how they fight each other, we’re just sort of caught in the cross fire really being another resource to be used by some of these critters. Which is why exposure is a good thing in some cases.
I remember once when me and my sons were sitting outside on the grass playing ball on a beautiful sunny day. My neighbor who had children about the age of mine looked down at me disdainfully out of her window and told me that it was disgusting to be playing in the dirt. I responded by telling her she needed to let her kids eat some dirt or they would never have an immunity. She all but bleached her kids. Seriously. They were never dirty, they were never outside making mud pies and running around barefoot in the yard getting sunshine and cool breezes.
Some years later after we’d moved away, she found me through a mutual friend of ours and proceeded to apologize to me for being so insulting (an rumor spreading back in the day to our neighbors about how disgusting we were). Her children are sick all the time. They catch every little bug that goes around and not only do they catch it they get the worst end of it every time which leads to other infections just moving right on in. They can never have just a cold it is always accompanied by ear infections and strep or simply evolves into worse things like bronchitis. Her doctor told her that they never had a chance to really build an immunity being so sparkling clean all the time which is what made her think of me. It was a very long conversation and now she is one of my top most customers when it comes to herbal remedies and homeopathic healing.
As the worlds microbes use us as resources, we have our own defenses like the other microbes to which they build resistances. It is good to get sick and actually just be sick until it passes instead of taking antibiotics and even herbal remedies meant to act in the same manner as modern antibiotics. We don’t live in a world that is conducive to letting things take their natural course on occasion and that is a large part of the problem as well.
Now, I’m not saying run out and get ebola and not get treated, but what I am saying is that minor and moderate colds shouldn’t be something we swallow a handful of pills for every time we get one to fight it off. Treating symptoms and letting it run its course will help us stay healthier. Sure its miserable but when you get a major cold or the flu you’re better equipped to handle it and that misery will be a bit lesser for it.