Certainty Effect
 (D1) Winning \$50 with probability .5  (D2) Winning \$30 with probability .7 (E1) Winning \$50 with probability .8  (E2)  Winning \$30 with probability 1.0
Consider a jar with 50 green balls, 30 yellow balls, and 20 red balls.
 Green  (50) Yellow  (30) Red (20) D1 \$50 \$0 \$0 D2 \$30 \$0 \$30
 Green  (50) Yellow  (30) Red (20) E1 \$50 \$50 \$0 E2 \$30 \$30 \$30

Most people choose D1 and E2.
but the payoff for yellow favors E1 over E2, but does not favor D1 or D2.
Going from Game D to Game E only makes option 1 more favorable..

In terms of utility:
If you prefer D1 to D2 then  .5D(50) > .7D(30) or D(30) < .7D(30)
If you prefer  E2 to E1 then  .8D(50) <    D(30) or D(30) > .8D(30)
Either one can be rational depending on your risk aversion, bot they can't both be rational for the same person.

The explanation is that there is a preference for certainty separate from the utility of the payoff.  D1 &E1, D2&E2, and D2&E1 can all be explained with different utility functions, but explaining the most popular choice cannot.