You’re creating an e-appeal, and suddenly you’re staring up at the north face of the 70,000-ft mountain you must climb. You have to write the subject line.

It has to stand out in the inbox, intrigue your donors, motivate them to act, and move them to click, but despite everything the subject line has to do, most self-appointed experts are unmovable on one thing: it has to be short, short, short.

“Keep it under three words,” they say. “Under two? Even better!”

But according to a study in which 12 billion — yes, billion — subject lines were analyzed, there’s no correlation between subject line length and open rates. Short subject line of, say, 12 characters, didn’t command people to click, but then again, longer subject lines of 150 characters didn’t repel people either. Subject-line length just didn’t matter.

So, how about this — let’s stop creating rules that are irrelevant to actual practice and restricting ourselves and hamstringing our appeals in the process.

We’re communicating with donors. So depending on a myriad of factors — everything from the offer to the nonprofit itself to donor psychology — there are times when a short subject line like “hey,” from the famous Obama email campaign, will work like gangbusters. And there are times when a long subject line like, “Fight killer diseases with your gift multiplying 50 times,” will get clicks like crazy. There is no empirically researched and optimized length for subject lines.

And that’s good. We should embrace the ambiguity and enjoy the process of connecting at a human level with donors. Because otherwise, fundraising would be all science and no art. And that would be no fun.