The best you can do about that is to sail a recent boat or a having a new car. Statistically they have less breakage than an older one. You cannot be prepared for everything or have spars for all things so in the end what it counts is your resourcefulness and creativity. Portuguese are quite good at that, that is so common around here that we even have a word for it that you cannot translate in any other language: "deserascar"
Seriously, if you think that a home made boat made by an amateur that never had made a boat before is more reliable than a production boat that has been made in hundreds of copies (whose eventual defects have been erased after the first dozens) and count with the accumulated experienced of a shipyard that has produced thousands of boats with similar characteristics and materials for many years, you are wrong.
I have a friend that has a steel boat made by himself. It looks like a true voyage boat , with windvane, solar panels, wind generator, two anchors on a double bow rudder, an adapted Mercedes engine and all the good and expensive materials. The boat costed him a fortune and he says very nasty things about plastic production boats.
We are both retired and eventually planned in sailing together next year. My boat is in Italy his was in Portugal and the plan was for him to sail his boat this summer to Italy, and eventually to cruise in Sardinia, for next year to sail with me in Greece.
He did not manage to go further than Valencia on the coast of Spain.
While I arrived at Rome, rigged my boat in a week and sail away to cruise more than 2000nm without any problem he took more than a month "preparing" his boat and then while cruising he had a problem with the refrigeration of the engine and had to call for help. Later he had a problem with the water tanks and had the boat flooded....he had more problems but I do cannot remember all. Anyway that is the main reason why he does not have made further than Valencia (where he leaved the boat for the winter)and that in two months of sailing. That and the boat being heavy and slow.
When I had my previous 36ft mass production boat I had done several times, in one and a half months, all the way to the Balearic Islands and back to Portugal and still had time to cruise slowly for three weeks on the Islands. Never had a problem that I could not desenrascar and always have done what I had planned.
A friend has a Sparkman and Stephens designed Hughs 31 which was mass produced . The tumble home on one side of the cabin is roughly 2 1/2 inches more that on the other side. Find one and check it out. That is typical of mass produced boats.
I met an old couple in Hilo who had crossed for mexico intheir brand new CT 41.They said itr saield fast but leaked like a sieve. What they had assumed was fibrglass was plywood and putty. Bob, did you design that one?
Anothe guy I met in San Quentin Mexico, who had draged in a hurricane there and was repairing the dammage said his mass produced boat was advertied as having 900 galons of fuel capacity. Instead she had about35 gallons of fuel capacity.
Mass produced means having a huge stake in saving a few ounces or an hour or two of labour anywhere, mutiplied by many boats, so they can to stay in business, something which is of little concern to a home builder.
Most home built boats are far better put together , even by first time builders, than most mass produced boats, for this reason. Anyone with a stock, mass produced boat who wants to test this out can tie their mooring gear to a home made one of my designs , built by a farmer wiht zero previous boat buildig experince , give her full throttle, with a large amount of slack in the mooring lines and see who's mooring bits pull out first, when the line snaps tight.
I believe the reason your friend's boat took so long and cost so much is because he didn't follow the directions in my book and plans , but got his advice from those trying to sell him expensive gear and materials. I wrote the book to help people avoid those pitfalls.
I rember back in the 80's building a boat for a couple who workred in an office doing gfovernment computer work. When I walked in in my work clothes the couple's boss took one look a me and took them into his office, and asked them "Is that your boat desgnber and builder?" they said "Yes." He said "I think you should shop around a bit more. " I built them a shell for a 31. He bought a new stock plastic boat. The sailed to California then down to Mexico and points south, thru the caribean to Halifax, back to the caribean for the winter, then over to England. After sevral years of this, they went back to Vancouver for a vist to find their boss stil working to pay for his boat ( and for having followed his own advice)