Not only was this a famous line from Yeat’s THE SECOND COMING. (“Turning and turning in the widening gyre. The falcon cannot hear the falconer; Things fall apart; the centre cannot hold; Mere anarchy is loosed upon the world, The blood-dimmed tide is loosed, and everywhere. The ceremony of innocence is drowned; The best ... ”), but it can also apply to long distance touring.
Generally things fall apart. A flat, a thrown spoke, loose screws, a sheared off bottom bracket.
The first thing you need is to have a few basic tools. Then you need to know what to do with them. My new bike (Torker) gets by with an allen wrench multi tool. You’ll also want something to true your wheels and tire irons/levers. Unless you’re going to Timbuktu or Tajikistan, you’ll probably not be too far from a repair shop. Some people take spare tires, I only carry spare inner tubes. I rarely ever patch while on the road.
You need to know how to fix a flat.
The problems that have occurred while riding, even if I don’t know how to fix them, I know how to diagnose them. Probably the biggest thing I’ve learned is how to work around problems. If my brake pads are whittled down to slivers, I know how to bring them in closer. When my wheel got out of true and the brakes were grabbing, I knew how to open the brakes up.
For catastrophic breakdowns there’s always hitching a ride with your bike to the nearest shop.
So, no, I’m no mechanic. I fake it a lot. The most important thing is to not let this knowledge or lack of knowledge deter you from setting out. I’ve learned a lot from hands-on necessity while on the road.