I'm about to do just that next week.
I hand over my keys, wander around locally for a couple of weeks tying up loose ends, then catch a ship across the Atlantic. My plans are open ended. I expect to be on the road for 18 months or longer and to have travelled as far south in South America as I can. At that point I'll re-evaluate and see how my budget/body/bike/desire is holding up and make some new plans.
I have research of a type done, I have preferred routes that I'd like to follow, with backups and alternatives. I've done a lot of practise the last few years, for example, camping in cold and inhospitable weather. I'm happy enough that I can deal with most things that will come at me, and that gives me the confidence to deal with unexpected things. But a lot I won't be able to appreciate fully until I hit the ground. My mind is open to significant changes to my "plans" on the road.
The logistics and bureaucracy is difficult, needs to be properly investigated and researched but is not impossible. Things like insurance were stressful to research and organise. I need to be sure that when I need it, it will work as I expect.
I am fortunate in that I am single and have no-one to answer to other than myself. In fact, that is probably the main reason I am doing this now. A partner willing to do the same is a rare creature. A secondary reason is that I reckon I have at least another 20 odd years of work in me. I'd hate to wait until I was retired and then discover that I was physically unable to do this or too embedded in my life to easily extricate myself.
I'm not wealthy in any material sense, but I have lived frugally and saved to give myself the chance to do this.
While I love to see parents and children touring together, I can't help but believe that there is a significant difference between going on a defined tour and heading away for an unlimited time. There is a different kind of psychology at play.