Don't mistake superstitions for reality. Even lawyers are terrible for this.

There is a general principle in law called estoppel, which means that if you tacitly allow something, you may not later be able to act as though you didn't. With patents that could mean that if you tell Big Yellow Widgets it's fine to make a thing that's clearly your patented Foozablip, but then after a year you say hey, Big Yellow, we just decided you owe us $50 per unit for the patent, estoppel might mean that's not OK. But it wouldn't mean Big Yellow can just keep making them without paying now you've decided on a fee, or that everybody else can join in too. Your patent still applies, it would just be unfair for it to override your previous OK and cost Big Yellow all that money.