A substitute Home Ec teacher. I was making a jacket with a very fine plaid. I matched and pinned the set in sleeves perfectly. Then after I sewed them in I noticed the darts were now in the front. She told me "you won't learn anything by ripping that all out. I've here all day with time on my hands let me do it for you." The next day I came into class to find them all ripped out and ready for me to start over. In later years she became me 4-H leader.
I didn't learn anything by ripping out but I sure got a lesson on kindness that has stuck with me for over 30 years.