When is quitting not 'quitting'?

"I found myself on stage in the middle of a scene about 'FPS games', which I found out later meant 'first-person shooter' video games, and I had absolutely no idea what was going on.  I thought to myself, I love Mozart and Shakespeare and I don't have the time or the energy to fill my mind with this shit."

This is what it sounds like when a great improviser quits the stage.

I turn 45 this year and I'm coming to grips with the oh-so obvious truth that there's a growing list of activities that I'm used to doing that in the future I will have no business persisting with.  I will have to quit.  I was lucky to see out an enthusiastically mediocre rugby career aged 30 without any lasting injuries (I wasn't good enough to warrant any special attention from the opposition) but that's it.  There's nothing I was doing at 24 or 34 that presently I cannot do at 44 but that cannot continue.

There seem to be four justifiable reasons for quitting something: -

1. You've succeeded
2. The world no longer wants what you do
3. You'd be an old fool to persist
4. Demonstrable hardship to your family

 The other reason is of course: -

It was too hard