Careful!! Check that pin

Gidday all, thought just share something with you.

Returned back to reality? last week after coming back from holidays.
Had a great trip going across to Charleville seeing our daughter and new born, onto Fraser Island, back via Longreach to see daughter 2 avoiding the rain as we went.
Continued upto Adeles Grove/Lawn Hill, Dooadgee (giddayJoe),across the Savannah Way, Lorella Springs making our way back to the NT.
Had a great time.
Every time I depart I always do a walk around the ute and camper to make sure everything is there.
Leaving Adeles we went the "back way" to Doomadgee.
After about 20km and several creek crossings I became aware of a banging type noise when I applied the brakes. I thought that by going through some of the creeks sand may have got into the brakes partially binding them. Continued on for a bit then thought better get and have a look. Checked the trailer, all looked good then checked the hitch and holy you now what! The receiver was sticking out from normal by about 10cm. The pin was missing and the banging that I heard was the trailer hitch moving inside the receiver. Luckily I had a spare pin in the tool box and no more problems.
But how did that pin come out? It could have been messy if the hitch came out.
I checked it before we left Adeles but I did not check that pin! But how did it come out? Did something hit the safety pin dislodging it then the main pin to fall out or........did someone need a spare pin for themselves. I hope like hell it was not the last one, if is is I would like to see there googangles hanging on a barb wire fence!
The moral of the story is do a proper walk around your vehicle and trailer and give it a proper check. If you hear an odd sound get out and have look.
Other than that the ute and trailer went well.............again.

Cheers
Greg