Karma, right effort, letting go, heroic sacrifices: what's the right thing to do?

Isn't there a story where the Buddha accosts a monk who's bleeding from performing walking meditation for too long, and tells him practice must be like a Veena's string - not too tight, not too loose? i.e the middle way Yet, I remember a story in the Dhammapada (Verse 1 ) about a monk who refused to take his eye medicine because he had vowed to not lie down for three months and remain practicing full time. Since the medicine wasn't effective unless taken lying down, he lost his eyes. The text says he simultaneously lost his vision and gained his vision - i.e. he became an arahant by practicing so arduously. The Buddha peeks into his past lives, and says Karma dictates that he must lose his eyes in this lifetime for sins of the past. It maybe so, but it was also his good karma to have access to medicine in this lifetime is it not? Leaving everything to Karma has me confused - because if that is so, then why practice, even enlightenment if it is in our karma will be obtained without effort. Gautama the Buddha was certainly going to become a Buddha, his Buddhahood had been foretold , so why did he practice? Second, what's with the open praise of macho effort right at the start of the Dhammapada? What happened to the middle way? This is not an isolated instance, there are several stories about heroic efforts from monks. The most famous must be the version where Bodhidharma plucks out his eyelids. There's also another version where he loses his legs to atrophy by not moving for nine years. I got to thinking about this after reading this question about monks and exercise. I am reminded of "A path with heart", by Jack Kornfield, where the author, himself a Buddhist monk under Ajahn Chah for several years talks about exercise and several other normal healthy things monks ignore in order to pursue enlightenment single mindedly. He recounts interviewing several monks who suffered from diabetes and other lifestyle diseases that came from not eating healthy food, from not exercising, from developing an aversion to their body and consequently not caring enough. I'm interested in hearing opinions in general, or an answer that can reconcile the two if possible. Thanks.