Hands down ride prep! With a wife and young kids, time is a RARE commodity in our house. In my wife’s mind I’m always gone “ALL afternoon” Despite my pleas that my actual ride/workout time is only a reasonable 1.5 hours on average (I agree with Midwestbiker that rides have to be at least 1.5 hours), even though it may take me 30 min to round everything up at times to go, 10-20 minutes to get to the trail, 10-15min to unload and prep before hitting the trail and God forbid if I ride with or run into friends to chat with for awhile (or have a couple post ride beers). Yeah, DEFINITELY ride prep!
Second is any mechanical problems that might arise to ruin the ride and all that prep…hitting that rock, root or drop just wrong and BAM! within a split moment your ride may be over and worse your next ride may be weeks and hundreds of dollars away! (My exact predicament right now)