The issue is that when you don't feel like you're achieving things at work, it's stressful.
At the end of a day when you worked on some task for a solid 8 hours, it's easy to unwind - work is done, work was accomplished, you know what you're doing the next day.
At the end of a day when you spent the whole day trying to find out what you should be doing, didn't find anything and will resume that the next day...you can't unwind. Were you doing the right thing? Maybe there was someone else you should've contacted? What if you don't find it tomorrow? Is the organization broken? Should you try to fix it? (No) - there's a lot that you can't help but think about it.
At the end of a day when you worked on some task for a solid 8 hours, it's easy to unwind - work is done, work was accomplished, you know what you're doing the next day.
At the end of a day when you spent the whole day trying to find out what you should be doing, didn't find anything and will resume that the next day...you can't unwind. Were you doing the right thing? Maybe there was someone else you should've contacted? What if you don't find it tomorrow? Is the organization broken? Should you try to fix it? (No) - there's a lot that you can't help but think about it.