The thing about unexpected lessons is that you never know what it is you'll learn, or that you had anything at all to learn in the first place.
In a quintzillion years, I never thought I would say this, but Donald Rumsfeld had a point, albeit a circuitous one, when he reeled off his screed about known knowns and unknown unknowns, and so forth, through every last permutation, down to the potentially uncertain but likely quite improbably unknown, but still completely possible, percentagewise, knowns. Or something.
Lessons are difficult, even if you're open and ready for them, and they involve small-beans issues like going to a different movie than you'd planned, or having to break down and order an alien beer or pop when your fav has been pumped dry at Drac's Stake-N-Steak or Burger Queen or Pasta Palace or whatever.
Much, much more seriously now: If you think such teaching moments and learning opportunities -- as we currently call Big Windows of Life To Go Look Out Of And See Something New -- are tough, imagine what the lessons are like when they rip your heart out.