As a high school teacher I had the luxury of long summer vacations if i was not doing summer school of some sort. Experience came with going longer distances. I remember my first cruise in our Hughes 22. Went from Whitby to the Thousand Islands in Lake Ontario. Got to Belleville and found out that you needed a few dock lines that were longer than 15', so a lot of it is just increasing the challenge step by step.
For cruisers on Lake Ontario, after you have done the standard trips (across the lake 20 to 50 miles depending on route, going to the Thousand Islands); the next step is to leave the lake and head, typically, toward the North Channel in Georgian Bay - this was tougher because you had to deal with the Welland Canal, long trips on Erie and Huron, and river currents against you between Erie and Huron. The next step was to go into the ocean. We went to a Nonsuch regatta on Martha's Vineyard (Erie Canal with mast down, Hell's Gate tides!!). Next was offshore, in our club there was a bit of a tradition of going to Bermuda for a summer trip (2 weeks to Bermuda, 2 weeks in Bermuda and 2 weeks back). At each stage there was a new challenge and more things to learn. Most people on Lake Ontario never leave it and are happy to do the same things each summer, but other options - in logical steps exist if you want them. I guess I was always building experience but very importantly you are building confidence to tackle something new.
Now we are aiming to go from Australia around South Africa and there are new challenges and experiences including longer passages in the Indian and Atlantic Oceans and the nasty weather from SW Indian Ocean around the Cape of Good Hope. I feel OK about it because I have met other challenges in the past that seemed just as big a step as these ones.
Finished the circumnavigation in early February in Grenada. Have to work on a book project for the next several months so the boat will be waiting for next year.