By observing multiple people who have done either thing for 10+ years.
Sure, there might be lots of confounding factors, and it might not be causation at all. That's why the quote is from a speech, not a paper
Here's another quote, I don't know if it's from a speech or anything:
> What can be asserted without evidence can also be dismissed without evidence.
Here's another quote, I don't know if it's from a speech or anything:
> What can be asserted without evidence can also be dismissed without evidence.