Almost all of us will have taken a mood-altering chemical at some time or another - i.e. what we call a drug. We've drunk coffee or tea, or had a few glasses of wine or beer. These are acceptable practices in terms of their health and social consequences.
However, some of us will have abused alcohol. Some will have smoked cannabis, taken amphetamines, ecstasy or heroin. This is dangerous, yet we choose to do this.  Why?

People abuse drugs for many
different reasons.

Here's a few examples:
To avoid feeling bored,
To fit in with our peers,
To have more self-confidence,
To belong to a special 'group',
To forget about problems,
To relax,
To feel good.

You'll note that all these reasons are about changing the way people feel. They're about avoiding boredom or loneliness, feeling powerful, or part of a group, feeling relaxed, feeling "good" etc.

Drug abuse provides 'good' feelings that are otherwise missing from a person's life

That's why people choose to abuse drugs - at least to begin with.