Anything that you spend a lot of time with can get boring sometimes, even if it's a great job or something that you love to do.
Playing scales on a musical instrument can be boring. Some football players love studying game film but for others it is simply a required task. Doctors read medical journals to keep up with developments in the field.
I use flash cards to memorize equities, hand ranges and different tournament situations. I have to force myself to study those things, but at a short table it's really nice that I know, for example, what the chances are that I have the only ace at the table.*
Anything that you do often can sometimes be boring. Doctors probably get tired of their hypochondriacal patients. There are times where a marathon runner doesn't feel like doing his 12-mile training run that day.
For me, poker is all about grinding, both playing and studying. But when I do the work, the results will come. Those results, in the form of dollars, make it all with it.
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*Five opponents is the breakeven point where you have a 50% chance of holding the only ace. You are more and more likely to hold the only ace as players are knocked out.
http://www.pokersyte.com/texas_holdem_poker_odds_2.htm