Sailing offshore means that you will be sailing out in the middle of the ocean with nothing but water all around you. As you sail, the scenery will consist only of waves. This may seem fun or interesting at first, but after a few hours, the monotony will bore you.
You might feel inclined to go inside or take a nap, not keeping a lookout as your boat sails itself. While this might seem tempting since there is obviously nothing around you, the truth is this is very dangerous.
When you don't keep a lookout, you run the risk of running into that one other boat on this huge expanse of open water. There is plenty of space, but boats paths will intersect, hopefully not at the same time!
Keeping a good lookout is vital to safely making ocean passages, but the truth is, you don't have to look all the time. What you really need to do is look most of the time.
The trick to it is to scan the horizon periodically for any other vessel and then go inside for a rest while you tackle some other aspect of sailing. Taking a break from looking will refresh your eyes so that you will be more alert to a new vessel in the distance when you look again.
To figure out how often to look, you need to evaluate your speed and your ability to see. You can only see as far as the horizon. When you look, you can see if there are any vessels between you and the horizon. If everything is clear, then you can relax until you reach the horizon again and do another lookout.
As you can imagine, this means that you will be looking around every 15 minutes or so, 15 minutes is not enough time for a good restful deep sleep, only enough for a nap. I like to refer to this schedule as "sleep sailing" where I have an alarm set next to me and I sleep at the helm.
The windvane is steering and the sails are balanced, so all you need to do is keep a lookout. You can doze off, and when the alarm goes off, you look around and make sure the horizon is clear, then go back to sleep.