Chains don't stretch.
Ok, not don't pull out the shotgun yet, hear me out.
"Chain Stretch" is a misnomer often used to describe the condition where the chain gets longer. What is really happening is that when the chain is made it is a series of links. pins, and sometimes rollers. There has to be a certain amount of play between the link plates and the pins to allow them to flex. For the sake of discussion lets say a new chain out of the box has a half a thousandths clearance. (Read that .0005.) As the chain is first used the initial wear within the pin and link area is significant (like breaking in a motor) so after a few hours of operation the clearance is now a thousandths. (.001) So you take that newly created clearance and add it up times the number of links (pitches) in the chain and you have a new length. So if you have 110 links and you create another thou per link you have added 110 x .001 =.110. Just under an eighth of an inch to the chain length. That is why you always re-check your chain and might make an adjustment within a relevantly few miles of a new install.
Now give me another minute...An eighth of an inch don't sound like much,
But now lets talk about chain lube. I know there are all kinds of new lubes on the market, dry lubes an such that are great at keeping your bike cleaner. However experience tells me that the primary job of a chain lubricant is to make parts slippery, right. Nope, it has an equally important function of flushing out the debris and dirt that is picked up as the chain goes 'round and does its work. IMHO, if there is not any oil leaving the sprockets and flying over the rear rim and the engine cases then there is no way it is flushing out the debris. Sooo, if the debris is staying inside the chain it is irritating the space betwixt the pin and link plate. Unlike an Oyster that creates a gem in an irritated space, that dirt will works its way around and before long that little .001 space now gets larger and larger. So now it us up to .002. 110 links x .002 = .220. Darn near a quarter inch. Little more dirt, little more time and you have a chain that is beyond it useful pitch because the distance between the pins has increased. Now that the chain is out of spec. it starts to eat at the sprockets. The radius of the inside of the sprocket pitch is machined to precisely fit the bushing or roller that is covering the chain pin. So as the distance 'tween pins increased it wears on the side of the sprocket.
Wax based and grease based chain lubes are excellent in an environment where dirt and temperature are not an issue. Like running a conveyor in an air conditioned factory. The work is steady, the temperature is stable and the chain stays clean.
Our chains are in the worst environment they can be in, dirt, heat, different loads at different times and the constant pull of over and under tension based on suspension travel. Even the load of one passenger vs two, or adding a sidecar.
Another enemy of the chain is heat. The running temperature of a chain ideally should not exceed 160 degrees F Above that, chain lubricant starts to thin, and the chances of it seeping out past the O-rings increase; eventually the film strength drops, don't forget the huge amount of centrifugal force as that chain whips around the end of the sprockets.
Even the cheapest chain without O-rings will last a surprising amount of time with proper care, meticulous adjustment and oiling at 350-mile intervals.
The average 110 link chain contains over 400 precisely machined components, well OK, some of the are stamped, but the stamping dies are incredibly precise and the tolerance of the stampings is incredibly high.
So if you want good chain life, use a good lube, use it generously and often. It costs less than chains. And tension it correctly. Chain too tight is worse than a chain too loose, especially in the first 350 miles.