I am a bit surprised by the responses on this thread. Yes, there is definitely a difference going from active elk hunting mode, climbing up the mountains and being active all day - to passive deer hunting mode, sitting in a treestand and doing nothing for literally hours at a time.
I just got done doing all-day sits for 16 days in a row (except for the day in the middle dealing with logistics and travel to hunt another state.) Outside of that, it was all-day sits for 16 out of 18 days.
I just figure the best way to kill a nice buck is to be on stand. Takes quite a bit of time and energy to hike in (20-60 minutes), setup the climbing sticks and stand (45 minutes), hunt for a couple of hours, and then take it all down again - just to do it again in the afternoon. Also leaves behind quite a bit of ground scent and disturbance.
If I have confidence in my scouting and know that a good buck is in the area, I have no problem sitting all day. If the spot is good, the odds increase of shooting that particular deer. On the rare occasion that confidence is not there, then I will relocate to an area where I know a good buck is in the area. But, that is rare.
To answer the question posed by the OP: how do I manage boredom? I really don't get bored on stand. Just stay alert. Unplug and don't think about life. Just focus on hunting and enjoy being outdoors. Many years ago I used to listen to sports on radio using a portable radio and earphones. Had a nice deer walk underneath me as my hearing was compromised - stopped using the headphones that day. That was about 20 years ago.