GET RICH :
If you haven't made your first million AND you can see how you own affiliate business could get you there
... then you shouldn't have general motivational problems.
If you are now working for yourself fulltime and you can compare how it was working for someone else in a dead-end job as a wage slave
... then you shouldn't have daily motivational problems.
THEN GET RICHER :
Then you realise that the first million won't do, there are always plenty of nice things to buy, houses, cars, trinkets, travel experiences.
So the next three to five year should be easy enough to motivate yourself with personal financial targets, and prize awards (perhaps 10-20% of profits spent on nice-to-have things.
Once you have earned enough to mean that you (and your significant other) no longer HAVE to work - then celebrate that achievement - less than 1% of the 1% get to this stage of financial freedom
BEYOND :
Of course if you are past that phase, if you've already made enough money to retire or live comfortably, then it IS harder, because if we are honest our affiliate endevours are like 99.9% of human activity ... completely pointless.
Now it's time to sit back, coast, or perhaps find people to help work in the business and do the bits that you don't want to - so that when you come into work all you have to do is a bit of management oversight and then work on the pieces you really want to.
A handful of people may want to kick on and create more-bigger-better affiliate business, but personally I have no desire to do so and you need to strive to get some work / life balance.
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SUMMARY :
IF you've made your fortune already - then working 10 hours a day / 7 days a week on affiliate tasks is silly.
Your motivational issues are sensible and it's probably time to scale back and outsource more (and just collect the money).
IF you haven't made your fortune yet - but are seeing the money start to come in - then knuckle down and get on with it.