I think it is because I don't have particularly strong nails, so they always broke very close to the flesh, so I'd have to do fingerpicking with my actual fingertips.
Most of the pain on the left hand, in contrast, was related to lack of muscle strength. After a few days of practicing it would be gone.
How much sunlight exposure do you get? My fingernails were also very weak until I started supplementing vitamin D, which made them grow noticeably thicker and stronger. I think a lot of people here spend most of their time indoors so they're at higher risk of vitamin D deficiency.