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Just a note, your rolls cover roughly the first 1000ft of the mile, and it is expected that you will continue to get similar rolls over the next 4000ft of the mile. Therefore, any constitution damage you take to succeed at your rolls shall be applied four times (You can make it about 1000ft before you're required to start making rolls, and I'm rounding for easier math).
As such, spending points to recover from 3 failures shall total 12 Constitution damage, not 3. (i.e. the number of failures x4.)