On paper, though, words can be burned to nothing or washed away in a body of water. The spoken word can be carried away on the wind -- and not so easily quashed or taken back. Spells can never be taken back -- even in the ritual burning of papers clearly stating the will, intent and function of the spell itself. That is just part of the visualization process.
I wrote a letter once (ooh, shocker. A writer writing an actual letter on actual paper...) Each word I put down was carefully thought out, almost in the same fashion as I would've written the first draft of a poem. I don't know if the person threw out the letter, or even read it -- but even so. Those words existed. Even as the paper crumbles to dust, turning yellow or being rained on in a recycle bin somewhere, those words exist still. I can only hope the meaning was experienced -- but alas. The meaning is wrapped up in the words. If they were read, they become a memory which is the words themselves as an image in the mind's eye and what they meant as more of an experience of emotion. If not, they stagnate, but the meaning doesn't ever get taken back.
I think spells work in a similar way. In enchanting things, you speak or think the words of intent into the object. Sometimes you can write a tag out for a witch's bottle and tie it or include it. Sometimes it's a charm or sigil protected by the energies of the caster. But these words, however they are made to be, remain.
Some of the most important words we save and keep to ourselves for fear of their meaning. Sometimes we save them for fear that those who hear them or those to whom they are directed towards will reject them. Maybe we fear that they will be turned around and used against us with intent that was not near the original meaning. But I think, if the words are that important, say them. Write them. Think them. Direct them. Don't hold them in. Sometimes words like "what if," are more difficult to bear than anything else.