In the old days, sailing ships carried carpenters, sailmakers, metalsmiths and riggers. If something broke, they repaired it or made a new piece from raw materials.
Times have changed. Modern recreational boaters don't need to know how to make everything, of course. Frankly, it would be impossible, given the broad range of technologies and specialized tools involved. Even propeller-headed uber geeks can't make everything they carry.
Nevertheless, and no matter what your level of do-it-yourself expertise, I think it's always worthwhile to ask yourself, "Could I make that?" Often times, the answer is an unequivocal "No!" But once in a while you encounter an opportunity to transform a frustrating "shopping" project into a fulfilling "fabrication" project.