Costly signalling
Costly signalling is the mechanism by which a message becomes believable because it visibly cost something to send, whether or not its content is read.
How it works
Words are cheap, so a claim on its own carries little weight. Effort is the one thing that cannot be faked cheaply, and a message that plainly took time or money to produce carries evidence of commitment inside itself before a single word lands. A handwritten letter moves people an email with the same content would not. Three hundred words of explanation beneath a headline signal that there is something to substantiate, even to the reader who never reads them. The signal works on the undecided most of all, and the talks give no threshold for how much effort is enough.
What it changes for a personal brand
Take the ten people whose attention would change your year and write to them in the way that would embarrass you to automate. One message a week that costs you an hour will outperform the hundred that cost you a minute, and you will know which is which by whether you could have sent it to anyone else.