Only law can change people's habits. Plastic cups example

Imagine someone telling you - plastic cups are forbidden in companies.

Yep. Coffee machine works only if you put your mug in. Crazy isn't it?

It happened in France.

Guess what. 

After a couple of wtf days, nobody really cares and get the habit to use mugs.

Imagine if a law has just "encouraged" this change.

People would have thought it was far too hard.

Only law can change people's habits.

I don't believe people - of course except a small percentage - can put constraints on them for civilization's survival.

You?