What defines a reasonable belief?When it comes to threats of violence or death and their legality, the concept of "intent" is in relation to the issuance of the threat, not intent to act upon that threat.
You might have absolutely no capacity to execute that threat, because you're sitting in a basement 2000 miles away from your victim. But if you lead your victim to reasonably believe you're watching them and able to act on that threat, that is what makes it criminally actionable. And your intent is only considered in relation to your choice to send those threatening messages, not your capacity to act. That is only measured in determining whether the target would have reasonable grounds to feel the threat was legitimate, so it has nothing to do with your actual capacity or intent to act, solely the target's reasonable beliefs to that effect.