So say, I am connected to the Twitch IRC and am in a valid channel. I have a basic script that goes:

Why is it that I can only trigger it on another client? If I try to trip it in an mIRC window it will fail. But if I'm in the chatroom on Twitch's side it will succeed.

I've been wondering this for a while now. Thoughts?

You can't trigger your own text events, simple as that.

But I can trigger them if I'm not under mIRC using the same account name and everything?

You can trigger it using your own nick as long as you're not using the same connection on the same client. (For instance the Twitch.tv webclient)

To trigger on your own text from the client's connection, you need to use the on input event.

For twitch, this is incorrect. Twitch doesn't send messages you send to different connections using the same account.

That is to say. If you have mIRC using the same account you are using from the webbrowser, twitch will not send messages you send from the webbrowser to the mIRC connection.

Hmm, you are indeed correct. This used to be the case earlier.
The case remains if you have two connections using the same mIRC client however. Connecting as the same nick on two different connections will display messages from Connection 2 to Connection 1.