Let's build a scene: I'm working on my laptop in the library, and while I'm gone to the toilet for 5 minutes, someone disassembled my laptop and took the hard drive. I encrypted it with VeraCrypt, so I assume it's save. Now, I build some PC's in the past, and a simple step involved in that process is connecting the hard drive or SSD to the motherboard. I was wondering this: What's the exact thing that prevents the thief from connecting my HDD to his motherboard and seeing the contents of it in Windows Explorer? (Or any other way)
Disk encryption provides data-at-rest security. That is, the data is only secure if your computer is fully powered down (or the attacker can't or doesn't know how to perform attacks against a live system). In such a case, the reason drive encryption is safe is that only you know your password. This password is used to derive an encryption key. The drive contents can be downloaded, but they would appear to be gibberish to anyone who does not possess the correct key.