It's often as simple as "does it affect your form?". If you tweak your ankle, and spend the next bunch of miles favoring it, you're moving stress and load from

It's often as simple as "does it affect your form?". If you tweak your ankle, and spend the next bunch of miles favoring it, you're moving stress and load from the part of your body that was trained to support that stress and load to some other part of your body. This can lead to cascading failures and more injury. Also "the wall" just means you didn't fuel correctly and now feel really tired/weak/etc. It completely sucks to be sure, but it's a "body" feeling, and not a "knee" or "hamstring" feeling at a specific part of your body.