My bike was making a rubbing sound....

.... but it went away.

     What a great photo. Imagine how long this took. The conditions would have to be ideal. No lube, a little bit of dirt to provide some abrasive, a broken shift cable, a limit screw just enough out of adjustment that the chain did not just drop to the small ring(Think about that. The low screw was tight enough to keep the chain off the small ring but slack enough for it to rub constantly), a very tolerant rider that could handle the constant racket without checking to see what it was.
     I am not putting this up to give the guy, that brought the bike in(For another issue), a hard time. No person is an expert on every subject, and the bike still moved when pedaled, and that was all it needed to do.
     This is really an issue of gradual change. We all experience change but sometimes it sneaks up on us(Where the hell did all that grey hair come from? Wait, where the hell did all that hair go?) If your bike has a mechanical brake system, think about change, then go check them. They can stand to be adjusted, can't they? The braking material comes off so slowly that we don't notice the lever coming in further and further. Then suddenly they don't work at all. That is how we look at any kind of failure, it happened suddenly. When really it has been in the process of happening for weeks, months or years. Happens with drivetrains to. It seems like one day it is working fine and then the next it is skipping and jumping. What really happens is, from the first pedal stroke, all of those bits are rubbing against one another and wearing out. Then after thousands of miles, one tooth on one cog is worn to the point it no longer can place the chain. Suddenly your bike skips. And I know you are thinking that there are a bunch of teeth to take the load, but almost all the load is taken by one tooth and roller on each gear. On a new drive train it will be the tooth at the top of each gear on the loaded side(More about this another time)
     When a frame fails suddenly, it is usually the result of months of propagation. You might have a flaw from manufacturing. That flaw could be a poor end cut on a tube or impurity in the steel.
     Some of you remember  the spoke fiasco of the mid 2000s, where hundreds of wheels just failed(suddenly), sometimes on brand new bikes sitting in the showroom. This was caused by impurity in the stainless steel spokes. The stainless had a mix of slag and ferrous steel in it and every spot of impurity was a stress riser. The spokes worked fine as long as you left them in a box, but as soon as you laced them in a wheel and put tension on them, a crack would propagate from the impurity and suddenly taco'd wheel.
     You can have a failure from a dent caused in a crash you barely remember(Meaning the kind of crash that was no big deal, not the kind where you are knocked out)

Ignore the crack and look at the dent. It does not look to bad, just a soft smoosh.(The customer hit a tree and managed to whack the bottom of the down tube against it.) This eventually went nearly all the way around the tube. That comes back to the sudden failure. The accident happened about two months before the bike came in. But it suddenly broke.

     This is the inside of that same tube. You can see that what looked like a soft dent, created a spider web radiating in three directions. That was the failure, it just took a while for it to get big enough to notice(and I had to cut the frame apart).
     Next time something just...breaks, think back thru the time line. Look for those cues to wear and fatigue. That is how you learn to spot problems before they turn your ride in to a hike.