When working to back up your thesis, you usually need to explain why you make the conclusions that you do.
Your reasons are the key to the veracity of your work, whether they be verifiable facts or sound opinions.
As you can tell from that, your reasons must be based on solid logic, either through detailed evidence or common sense.
To be sufficiently logical, you will likely need considerable support, authoritative sources and believable accounts (not to mention, a sensible writing software).
Suffice to say, you can't simply throw a made-up statement and expect your audience to embrace it accordingly.
Common Sense.
If you're stating something that's common sense, it can often stand on its own.
To be thorough, you can cite regular events where the idea makes perfect sense or list down anecdotal accounts.
Hard Facts.
If something is a hard fact, make sure to cite your sources.
The more authoritative and scientific the source, the stronger an argument it will hold.
Of course, even facts will not convince some people.
Do note that you don't have to sway the ones who willfully defy logic.
Opinions.
An opinion is a personal stance.
As such, it can't stand on its own as a logical reason.
They need to be supported with hard facts and other evidence to be able to convince a reader.
You can also use emotional arguments if you know your audience well.
Bear in mind, however, that an argument like that won't stand up to deep scrutiny.