Profitable, hard and important.
They can's exist without the other.
If it's profitable but not hard, it'll stop working sooner or later because everybody will end up doing it.
And if it's hard but not profitable it'll stop working because you'll sooner or later not just run out of money but also out of energy.
If it's profitable but not important it's likely that you'll lose interest at one point.
And if it's important but not profitable it'll stop working because you'll run out of money sooner or later.
And the list goes on and on and on.
One can't exist without the other.
So which one are you going to choose?
P.S. Profitable and important is probably the hardest of it all...