How long does it take for you to internalize an attitude/mindset and think that way automatically?

This is a really obscure title, I know. I’m not sure how to word it. But I think it would help if I began with a story:

I was in Wal-Mart today. I bought a good deal of junk food and some toiletries. When the cashier handed over the receipt and moved on to the next customer I noticed she’d split my purchases into two plastic bags.

At this point I realized how much my parents have instilled into me a sense of frugality and aversion to waste (which the whole eco-friendly craze agrees well with) because I thought, “Why two bags?”

And since she was helping the next customer I ended up shifting everything into one bag (she’d divided it up so one bag was food, one bag was my toiletries) and going off. I’m pretty sure everyone else thought I was being too obsessive.

The thing is, this isn’t something I would’ve done a year ago. A year ago I wouldn’t have noticed I had two bags. I wouldn’t have thought about the pile of plastic bags I keep on acquiring. I used to have to consciously remind myself to be ‘green’...now I do it automatically. It’s interesting.

Have you ever tried to change your way of thinking or the way you go about life (being less judgmental, more environmentally conscious, less confrontational)? How long did it take for you to do that naturally?