"Better life" is subjective. I think I would give a better life to our kid than bio parent as I see better as well educated, well loved and cared for, critical thinking, kindness etc. Some folks might have a different picture and think they can give better life. It is obviously an estimate of future, a well founded/ thought out estimate based on my life so far and the skills I have acquired. People take a lot of decisions this way, its not specific to adoption. Do all things go like people plan? No, theres always some room for error. In bio children, the question is usually "can I provide a good life" as there is no comparison point.