Trying to collect some common mistakes / misunderstandings in the ownCloud community or during the oC usage in here.
Can i use ownCloud as a backup for my data?
oC is not designed to be a backup solution. So the simple answer is: No
The reasons for this are described here: https://owncloud.org/faq/#backup
Is the encryption app protecting my data on my local hard disc (e.g. from server admins)?
The encryption app is designed to protect your data on external storages (like Dropbox or Google Drive). It is not designed to protect your local stored data from admins having access to the server. The reasons for this are explained in the first red box at https://doc.owncloud.org/server/9.1/admin_manual/configuration_files/encryption_configuration.html
Why is the installation of ownCloud that complicated?
The installation of oC itself is quite easy. Download the oC files, extract them into the folder of your webserver, run the installation wizard and you’re mostly done.
However you should note that the prerequisites for ownCloud (consist of a Webserver, PHP and a Database) obviously needs knowledge about these components. If you want to run ownCloud you need at least basic knowledge about these mentioned components as well as Linux knowledge. But that is true for every web application out there. 
Which are major releases of ownCloud?
A common misunderstanding is, that e.g. 8.1 is not a major release. This is plainly wrong as the versioning scheme was changed during the release of 8.0. So the following for example are major releases:
7.0, 8.0, 8.1, 8.2, 9.0, 9.1 etc.
Is it safe to upgrade to the new release?
All code entering ownCloud has been reviewed twice as well as tested by both automated means and through the efforts of volunteers. Releases are done only when all issues we are aware of are fixed or can be mitigated easily. In short, ownCloud releases are always as stable as we could make it without your help. If you want the guarantee that it will work in your specific situation, make sure you help test before a release is made so your issue can be fixed in time.
(Copy’n’pasted from https://owncloud.org/faq/#upgrade)
Additional note: ownCloud is quite complex software so it is impossible to test it against every environment, server configuration and special use case out there.
Why should i do backups before doing updates/upgrades? Are you not testing your releases?
As already explained above ownCloud is a quite complex software and it is impossible to test it against every environment, server configuration and special use case out there. Thats why it is absolutely mandatory to do backups to be able to restore your oC instance if something went wrong during the update/upgrade.