There have been many studies on this subject and the simple answer is that addiction is not caused by just one fact. Addiction is considered a bio/psycho/socio/environmental disease. Just having the gene for addiction doesn't guarantee that you will become an addict. Neither does mental illness or being subject to mental abuse as a child. Addiction is usually the result of a combination of factors that include genetic predisposition, the way the person see and interacts with the world and their ability to cope with stress, and the person's physical environment while growing up. Kids who grow up watching their parents abuse drugs or alcohol are much more likely to do the same thing.
Yes it is a factor.
A stimulus is a factor that causes a response in an organism.
Gyres are caused by wind current, like the Coriolis effect. The rotation of the Earth plays a big part, as does friction of the waves and underlying ocean bottom.
a strong personal commitment
yes
It could be anything from pressure to the first try.
they died
Value for money.
limiting factor
I suppose you could use improper factor, but the for any given integer, the factors that are not proper are known as trivial.
Suppose p(x) is a polynomial in x. Then p(a) = 0 if and only if (x-a) is a factor of p(x).
Social learning is considered the most important single factor in addiction. It includes patterns of use in the addict's family or subculture, peer pressure, and advertising or media influence