My physical condition, I must say.
I'm physically "fit", as in, I can meet and surpass all the physical standards (Express and BFT), but in the long run, I've got some serious physical issues.
For starters, I have completely flat feet. This makes ruckmarches and morning runs difficult. My condition also lead to damage to my knees. For this, I was recoursed in Basic. I barely made it through the second time around. Four months later, I've developed shin splints. This is excruciating for the same activities (ruck/pt). This is unfortunate, as I have SQ coming up in a couple months (after I finish Phase1 of my QL3's). The good news is that there is no SQ until early/mid February, so I have the Christmas break and then some to get these issues sorted out. Such means would be as simple as reducing the high impact activities, building up my quads, buying new shoes/finding better orthotics and rest, most important of all.
Overall I don't think it's anything I can't overcome.