This command combination sorts mirrors and then performs the update. Sometimes a mirror might be temporarily unavailable for a number of reasons. Quite often it might be a problem somewhere between your machine and the mirror(s), or an issue with the mirror itself.
There are potentially many reasons why a remote peer might be disconnected. If updating via WiFi, for example, the likelihood is high that there might be an interruption during updating. Always use a wired network connection where possible.
To help minimise the issue you could arguably use the same command combination every time you perform an update.
This is where expectation meets reality. I’m afraid that Linux demands a certain amount of maintenance to be performed by the User; a hands-on approach; despite the usual blurbs one might read. This is the best way to maintain the ‘just works’ ideal. 
The Manjaro Wiki shouldn’t stress or worry you. Even if you refuse to learn commands, it doesn’t take much effort to bookmark (and/or print) instructions and commands commonly needed. Then you can use them as a reference whenever the information might be needed.
Hi @Horizon and welcome to the Manjaro community.
As a new forum user, please take some time to familiarise yourself with Forum requirements; in particular, the many ways to use the forum to your benefit:
To that end, some or all of these links may be invaluable:
- How to Post
- How to Request Support
- Manjaro Wiki
- Tutorials Useful guides can be found in this category
Last, but not least, the Update Announcements, which you should check frequently for important update related information.
An issue may be directly related to a particular update; these announcements should generally be checked before posting a request for support.
I hope this is helpful.
Cheers.