Doh!

I was (ever so coolly) digging at our ward's National Day of Service service project.  I'm thinking I'm pretty hot stuff.  I can dig with the best of 'em.  Why don't I take a little water break and stick this shovel in the dirt while I rest.  I'm as strong as anybody, no problem... SLAM!  Problem.  My shovel bounces off the dirt and bark, vibrating my entire body.  While penetrating said dirt not one centimeter. What, in my coolness, had I failed to note?  I was digging with a flat edge shovel...