I may have lost some of youth's sharpness, and I may be stranded in an alien world, but I am no fool.
Just because I've been stuck in this alien world for the last few years doesn't mean I'm a fool. 
mnli hypothesis: Just because I've been stuck in this alien world for the last few years doesn't mean I'm a fool.  premise: I may have lost some of youth's sharpness, and I may be stranded in an alien world, but I am no fool.