What's interaction effect?

from Dr. Sakamoto's lecture (Oct 4)

Y=a+bX+cW+dXW

Where
Y= your degree of angry
X= boyfriend forgot your B'day  --> probably not that matter, sometimes he forgot
W= boyfriend had a dinner with his ex-girlfriend --> just a dinner, not a big deal
XW= boyfriend forgot your B'day and he had a dinner with ex ON THAT DAY!!

Lets imagine how big, oh lets use "significant", the effect of interaction term will be!

Economics vs Sociology

Economics is all about how people make choices. Sociology is all about why they don't have any choices to make. (Duesenbeny 1960)