You have to use the right form, as there's usually only one or two ways to do an exercise correctly.
You have to do the right exercises, in order to prevent injuries from imbalances and asymmetry.
You have to eat the right amount of calories, too little and you won't gain muscle, too much and you'll start putting on too much fat.
It offers a reassuring certainty in a world where not much is certain anymore. It's also the perfect sport for people who like numbers and spreadsheets, as it's the only way to consistent progress. Because of all this, success depends solely on your dedication and determination, which is pretty cool if you ask me. This also makes it incredibly difficult at times.