How long can you grind?

I'm curious to know how long people can grind before getting bored. And what keeps you motivated to grind?

I used to be able to grind for hours years ago, getting 7% on my f/p mage at lev 6x but now training is like... ugh

Average 3~5 hours w/o 2x EXP card. If there's 2x EXP event, I'll buy 2x EXP card and grind 5~8 hours and sometimes change user.
(P/S :MapleSEA's 2x EXP card isn't 4 hours but 24 hours.)