The tribe or the person?
A parade of tourists is going to walk past your store today. Each is a separate opportunity for you to tell a story, to engage, to make a sale.
A connected community of readers is going to read what you wrote today. A cultural shift will occur among a small group of people because they will share, discuss and engage with each other about what you wrote.
Here's the key question: are you trying to change an individual or are you trying to incite/inspire/redirect the tribe?
Direct marketers traditionally deal with separate events. Each catalog, each clickable ad is a unique transaction. In the world of separates, the simple test makes sense. You don't pollute the pool when you try different transactions or different products with different people.
If you focus on individuals (and many marketers do) then the rule is: treat different people differently.
On the other hand, many marketers deal with culture. You put something into the world and it won't work until it 'catches on'. The goal is to catch on with the herd. Catching on isn't a 1:1 private transaction. It's a group phenomenon, a place where you don't get a second chance to make a first impression. The simple test makes no sense here–it's either good enough to spread or it isn't. There aren't as many distinct threshholds, because the culture shifts or it doesn't.
When I ran Yoyodyne years ago, all of our email campaigns were aimed at the person. It was before significant online sharing, and we could measure one by one how people responded to our work.
At the same time, our backers and our clients were very much part of a tribe. We needed to change the way an entire industry thought, not merely make one sale at a time. It took me a while to realize that I had to market differently when I was trying to change the way the group thought—treating the tribe using individual-person thinking almost always backfires.
Or consider two non-profits. One wants to change only those it serves and those that fund it, one transaction at a time. Those are person effects. The other wants to change society, the culture, the way philanthropists think–those are tribal effects.
Many marketers, particularly bootstrappers and freelancers, rarely have the resources to invest in tribal effects, particularly among customers (as opposed to funders or employees). They don't have the resources or the leverage to make unmeasured investments that one day will pop into a change among the entire tribe.
The flip side, if you seek to change the culture (or a tiny tribal element of the culture), your timeframe and what you measure have to be focused on the conversation, not the individual.
If you're tracking landing pages and conversions and even market share, you're probably in the business of working at the person level. The more difficult, time-consuming, unmeasurable work involves creating ideas that spread among the tribe you target.
To change the culture, change the conversation.