The video below does a reasonable job of explaining the high-level concepts of why it was safe for me to post my public key on a web page:
A lot of this stuff is counter-intuitive and hard to grasp when approaching it from a traditional ‘exchange of secrets’ point of view. The analogy to paint makes it obvious, and negates the need for having to grok the maths involved… well, unless you feel like understand and auditing the implementations.
One of the cardinal rules is that you should never ‘roll your own‘ when it comes to cryptography. There is almost always someone, or some group of people, that have better odds of getting there without making beginners mistakes.