Necessity is the Mother of all invention

Learning from your (or other people's) mistakes can be the greatest way to increase your organization.

The first time my husband and I took a plane trip after we had our oldest daughter, I learned a BIG lesson from the family traveling with their young toddler who were sitting behind us.

Of course, I had packed a ton of diapers, wipes, snacks, comfort items, etc. Now however, I NEVER travel without a change of clothes for EVERYONE in my group in our carry on luggage. Why???

Upon decent, our fellow family travelers learned that not only did their son get air sickness, but that he would projectile vomit throughout that sickness. I was sitting RIGHT in front of them, and I was very worried that it was going to hit me. Now, the lesson I learned was not from that horrible experience, it was when I saw these poor people walking through the airport and waiting for their luggage COVERED in vomit. If there was a change of clothes, and sealed bags to place them in (if you don't choose to just throw away everything), they wouldn't be walking around soaked and stinky.
What lessons have you learned from your mistakes or others. Obviously we can learn from MUCH smaller examples, but this one will always stick with me.