You can’t teach an old dog new tricks. This does actually have a scientific basis, animals lose neural plasticity when they mature. Human adults retain some neural plasticity and are much better at learning than adult animals.
Laughter is the best medicine: Nope, tried it, drugs are the best medicine.
Sunlight is the best disinfectant: Nope, tried that too, disinfectant is much better.
The pen is mightier than the sword: Haven’t tried this one but I’m pretty sure that swords are better if you want to stab someone.
Running a triple clamp fork on a hardtail will cause the headtube to break off and you’ll die.
I’ve seen it happen, although he didn’t die, he just limped a bit.