Only a very naive hiker puts down a pack and walks away from it. Stay with your gear!
I think it would be better to phrase it as "Only a very unprepared hiker puts down a pack and walks away from it."
Setting a pack down while out hiking to explore around is very common. However it is incumbent on the person(s) to ensure that they always have basic survival gear in their possession at all times and that they are also dressed for the expected terrain and environment.
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Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.
John Lubbock