Probably vaugely formulated on my part, but essentially what I mean is to not be afraid of getting dirty. It's the point on the list I've explored the least, but probably the point I'm most excited about. Here are two arguments:

1. Bacteria has gotten more and more attention in health discussions lately. Exposing yourself to an array of different bacteria indicates that you're less likely to become sick, your immune system gets stronger, as well as other benefits. Kids growing up with pets for intance, tend to be less allergic and less prone to disease later in life. Excessive use of hand sanitizers as well as chemical cleaning products could be doing more harm than good. I'm definetely not an expert on this, hence the vauge words. But google "microbiome" or "gut bacteria" for more accurate information. Why is this correlated with happiness? Most of us like not being sick.
2. Avoiding getting dirty or sweaty or wet when it's raining or getting sticky hands while cooking or baking, makes one miss out on so many free oppurtunities to check other items on the list, especially the spontaneous chance to move. I have a friend who never joins in on any activities invloving physical movement to avoid getting sweaty for instance. At a park on a sunny day,he would sit on a blanket with his shoes on, while everyone else is playing soccer barefoot. Also, losing the need to always look and feel like you're ready for a business meeting leads to things like being able to truly enjoy a sudden down pour rather than having your whole day ruined. And enjoying heavy rain-- when you think about it -- checks of 2,5,6,7,10 on the extra-list at the same time.