I recently replaced an exterior door. I probably watched the same Youtube videos. It took me all friggin' day! The next one will take half that time easily, because once you've done one, you've pretty much figured it out. But that first one ...
I did have some not necessarily common complications. The old door was a smaller non-standard size, even thought the rough opening was a standard size. So I had some minor reframing, and I had to remove, cut, and replace some vinyl siding. This was also an exposed exterior door, which meant I had to fabricate a sill pan, replace some bad house wrap, and flash. I also got to learn how horribly wrong the previous door was installed. House wrap wrapped right into the house at the top. Zero flashing. No sill pan. The entire door and sidelights were held in place by the brick molding's itty-bitty finish nails. I removed the brick mold on the outside, and the whole thing just about fell on me. Wasn't expecting that.
Basically, hanging a door is one of those jobs that seems like an easy 2 hour job. Then 3 trips to the hardware store and 6 hours later you're still trying to figure out exactly what went wrong. I'm glad I did it. I learned a lot, and more importantly, I know how a door should be installed. If I could assume hiring a pro for $150-$200 would get it done right (which is a bad assumption around here), I would go the pro route in the future.
