From The Top Ten Distinctions Between Millionaires and The Middle Class by Keith Smith, P 7.
"When I ﬁrst started thinking year to year, my income really started to increase. I asked myself questions like: How can I double my income this year? How can I legally pay less in taxes this year? As I have seen this principle of long-term thinking in the lives of my mentors, it has challenged me to look further into my future. I now have business plans that go twenty years into the future. I spend time on a regular basis thinking about what I want my life to be like ﬁve, ten, and twenty years from now. Then I create plans for how to get there."
When he says (I have seen this principle) does he imply something like (I have seen the [effect of this principle... in the lives...]?
Is he talking here about the effect or what?
Please rephrase the sentence to better understand it.