There's no question that spending time in the great outdoors can teach you some serious lessons...and some not so serious ones, too.

What's the strongest lesson you've learned during your time in the backcountry?

The strongest lesson I've learnt is not so much of a lesson, as a reinforcement of the way I think. Relax. Observe, think, decide, act (the good old OODA loop). Being outdoors goes beyond a lot of people's comfort zones. Fear and panic can take over when people feel like they are losing control. Think, focus, refer to your training and experience, then deal with any problem.
It's kind of a zen thing. In my army days - this was a central tenet of getting things done. In one of my alternate lives (apart from being out bush) as a commercial diver - this philosophy keeps you alive. If something goes wrong, but you are breathing, there is always something you can do.
Drama aside, I think this feeds back into a general outlook on life. Control what you can and stack the odds in your favor (training, practice, mental and physical preparation), but don't stress the things you can't control. Just deal with it.
I think you'll live longer and happier if you do. The necessities will be taken care of intrinsically, and you can enjoy the things you went out bush to do.

Backpacking isn't accomplished on the internet.

Pay attention and be observant. Just hiking along in a fog of music, fatigue, whatever leads to two things. First, that's how people become lost or injured. Second, you miss so much if you are not aware of your surroundings--which, hopefully, are why you are out there in the first place!

That my best hiking partner is my wife. And there is no better way to spend time than with her in the Wilderness.

Omar Khayyam was right!

That I'm never quite sure whether I've got 35 years of experience, or 1 year's experience 35 times.

Never follow too closely behind someone using trekking poles...