Interesting that you said this....I did a teaching practicum in India for approximately 2 months (and an extra 1 month of travel). It was an amazing and eye opening experience in terms of consumption and the way that other people live. I would say, in my estimation, that it impacted me deeply forever, but on the surface for only a few months after my return. What I mean is this - when you are there and surrounded with the realities that many people face every day, it does make you re-evaluate your life and your belief systems in relation to how we live in the West. You begin to notice how many things that we have in relation to others and when you return, you really are so thankful for everything (hot running water, for example). However, after a few months, you 're-climatise' to your surroundings again and the reverse culture shock wears off.....which means you go right back to the same as before. I think lasting change can't come from external exposure, no matter how shocking and (oftentimes) upsetting it is at the time (and so many things that I witnessed were shocking or upsetting). I think that in order to last, the change that we seek must be obtained in relation to the lives that we live in our every day surroundings. We adapt to our surroundings, so this isn't surprising to me. I think the gulf between intention and actualization is sometimes huge and overwhelming, and it can be complicated when commitments are made when we aren't in our regular 'habitat' so to speak. This was a struggle that my peers had as well, and we had so many conversations about it during our time together. I'm not saying seeing the ways that other people live doesn't impact a person, but I think the impact wears off after a while once we return to the comforts of home.
Interestingly (but not surprisingly!), the people with so little in India (including the kids that i worked with!) seemed happier than people I know here in Canada. That is because in the town where I worked, the feeling of community was prevalent - and as we know, good relationships are a key to happiness.
Just my two cents based on my experiences though!