When someone stops replying to me I figure they either ran out of things to say or whatever I said last wasn't worth a reply. And if it's a first time message, either they didn't get it or didn't care enough to respond (in which case it's no big loss for me).
Funny, I actually messaged someone for the first time on Monday morning. In the past I would have been beating myself up if he/she* didn't respond in 24 hours. Now my fear of internet rejection is somewhat less, and my excuses for why he/she* didn't reply seem more plausible. The fear of not being good enough for a reply is still there, however; it's just not as great as in years gone by.
* For legal purposes the sex, gender, and/or gender role of the person herein being discussed has been purposely disguised. This post in no way seeks to blame anyone for considering the poster as less than qualified for any position or role set forth in the aforementioned message.