The most tragic thing is that the world is more nonlinear than we think and it can not be expressed or described in a words.
With linearities, everything seems clear and constant. An increase a variable will increase the result. for example: an increase in investment will increase the rate of return, a 10 percent increase in money in the bank corresponds to 10 percent increase in the interest.
But in real life, its not that linear. Think of our struggle in getting satisfaction with everything we do. Think of the result as compared with the input we put in. Think of our improvement and the effort we put in. Does that sound linear? Not in my case.
Linearity is just an exception; non-linearity is the truth.