The question we get most from first-timers is some version of "am I fit enough?" The honest answer: general fitness helps, but altitude sickness has almost nothing to do with how many kilometres you can run at sea level. It's about ascent rate and hydration, which is why treks like Kedarkantha build in a deliberately short, easy second day — not because the trail demands it, but because your body needs time at altitude before it climbs higher.
Nobody mentions how cold camp gets relative to the daytime trek. You'll be sweating on the trail by 10am and layering up in a down jacket by 6pm at the same campsite. Pack for both extremes, not the average.
The food surprises most people. Trek cooks on Himalayan routes are genuinely good at what they do with a two-burner stove and basic supplies — dal, rice, sabzi, and usually something fried and unreasonable for morale on the last night. Nobody is eating trail bars for six days.
The actual hardest part of a first trek is rarely the summit push itself — it's the 4am wake-up in sub-zero cold to start it. Mentally preparing for that specific fifteen minutes, not the six hours of walking after, is what most first-timers underestimate.
Last thing worth knowing: a good trek leader will make a hard turn-back call before you'd make it yourself. If your group is asked to skip a summit attempt because of weather or pace, that's the system working, not a failure.