Sleep Quality: Seven hours of good sleep beats eight hours of restless sleep every time. If you slept poorly, reduce intensity that day.
Stress Levels: Physical and life stress compete for the same recovery resources. That work deadline is literally affecting your squat numbers. On high-stress days, focus on movement quality over intensity—think 70% effort instead of 95%.
Nutrition & Food Timing: Recognize when you're running on fumes. Evening workout but haven't eaten since lunch? That's a performance limiter, not just a comfort issue.
Hydration: Even mild dehydration can tank your performance before you feel thirsty. That sluggish feeling might not be fatigue—it might be that you've only had coffee since breakfast. (there's also such a thing as overhydration)

Honorable Mention: Past Injuries

This one's not universal, but if you've got old injuries, they'll influence your training. Listen to those early warning signals—they're your cue to warm up longer or modify movements.