If I had to name one quality a motorcycle builder needs it would be persistence. Determination. Dogged determination. Building a motorcycle is a big undertaking. It takes a long time. There will be many challenges along the way. Things will go wrong, or maybe even just less than perfectly. Maybe that frame tube is bent just a degree too far. Maybe you've spent days grinding a frame until every speck of rust is gone and every weld is smooth. Or you've been sanding and polishing an aluminum tank for days and it's still not done.
Persistence! That's what it takes to make a beautiful motorcycle. I guess you could cobble together an ugly motorcycle with less persistence, but even then it takes a long time. It's persistence that allows you to refine and correct, to start over when necessary, to keep sanding, to keep working on tiny dents or scratches until they're gone, to keep polishing until the tank glows.
I guess if I were to generalize from this, I'd say persistence is what allows you to accomplish just about anything of consequence in life. Almost nothing worth accomplishing is easily done. But just because it's no easy doesn't mean you can't do it. Just persevere.