Everyone has written it. The reply after the meeting that went wrong, typed straight into the box at eleven at night, read twice, deleted. Not because the words were false — because sending them costs something tomorrow that they are only worth tonight.
So write it here instead, where sending is not on the menu. The button does the only thing it says. While the letter burns you can open the network tab and watch: the only traffic is the analytics tag counting a visit, and it never sees a word. Spellcheck is turned off on purpose — some browsers ship what you type to a server to check it, and this page promised you nowhere. When the burn ends, the text is gone from the page and from memory. There is no undo, which is the feature.
The unsendable version is the one that helps. Writing it — actually writing it, not composing it in the shower — is what takes the charge out, and it works better when you know for certain nobody will read it. The polite version, the one with a future, can be written tomorrow. It will be shorter.