In weight training, there are two predominant modalities.

Lifting for strength and lifting for hypertrophy, aka, muscle building. There's overlap between the two, but the majority of the time it's better to specialize in one or the other for a particular training cycle.

Either way, progression is key. How to structure and think about that progression varies considerably though.

For strength, iteratively maximizing the weight on the bar is the goal. That's obvious.

In contrast, in bodybuilding, while lifting big weights is still awesome, the goal is inverted. It's stimulation of the target muscle with the smallest effective weights possible.

Yes, smallest. We'll get back to that.

But first, it's important to clarify that over time, in both modalities, there's no getting around the need to move bigger and bigger weights more proficiently.

And, the strongest, most jacked people on the planet are 100% tossing around nigh-superhuman masses like it's just another Tuesday.

However!

In the context of training, the weight is not the point for either goal.

See, our muscles and nervous system understand tension and leverage^[1]. Despite the assumption of every noobie lifter ever (especially the high school dudes), we don't have a "weight on the bar sensor" built into our musculoskeletal chassis.

So, while moving bigger weights over time is crucial to both, it's an indicator of success, not success itself.

To wit, it's trivial to imagine a scenario in which someone adds weight to the bar week after week without getting stronger. It's called a quarter squat.

Similar scenarios for muscle building abound.

To speak the language of the musculoskeletal system then, you need technique that allows reproducible reps and progressive over-stimulus.

For strength, that means moving bigger weights consistently for years with said quality technique. This maximizes stimulus potential and minimizes injury risk.

But what about that nonsense, "smaller weights are better for muscle building" bit from earlier?

Here again, the weights aren't the thing driving progress; they're the shiny object designed to waylay the egotistical lifter.

It's not that the point is to lift small weights. The point is that how the successful lifter thinks about it is inverted.

With strength training, you want to make a heavy load feel as light as possible. You do this by distributing it, with the best leverage, across as much muscle (and bones and joints and connective tissue) as possible.

The local failure of a muscle, while inevitable at true max efforts, is always to be avoided.

In contrast, with hypertrophy, you want to make the smallest effective load feel as heavy as possible on the target muscle.

Local failure is the name, underwriter, and owner of the game.

Note the key word here is "effective." If you get the intended stimulus from 50 kg and from 70 kg, why would you ever use 70 kg unless driven by ego (or the odd bit of fun)?

So, to recap, strength training; big weights over time. Hypertrophy; smallest weights with optimum stimulus over time.

Not opposite processes; inverted.

Confusing which stimulus you're after is an evergreen gym mistake we all make at some point. Probably many some points.

And while I find concepts gleaned from training interesting all on their own, I'd wager that getting the mechanisms for success and its external indicators confused is a surprisingly universal insight.