"We teach best what we need to learn most."
What happened most recently to you that confirmed teaching is the best way to learn?
In my course called Jamming for Advanced Beginners, a message I try to convey to guitar students early on is to avoid thinking of any improvised note as "right" or "wrong". Better - I coach them - to consider the notes they intended to play vs. those they didn't intend to play. I strongly believe any student who fully internalizes this critical lesson will be a more relaxed improviser from the start. In addition, having this kind of attitude about one's own improvising is a surefire way to ensure that person will be far less likely to harshly judge what other people play in their early attempts at improvising.
If I could borrow that HG Wells contraption, I know what point in time in my life as a musician I'd return to. I'd go back to my start as an improviser and hear my own words endlessly repeated back to me: "There are no wrong notes, Pat, only notes you didn't intend to play." Perhaps those words would have given me enough confidence to ignore anyone who cringed at something I tried.
But time machine fantasy aside, what I've seen - as a teacher - is that each time I repeat this message, an unsurprising thing happens; my own improvising gets a little more relaxed and natural. And that's when Buddha's words are confirmed for me, yet again.