Sometimes in life it's difficult not to get carried away by wanting things and not really understanding why. What you want could be something material like a new car or even something situational like wanting to be able to do what someone else is doing at a given time. We desire what we don't currently have but often this is actually just the product of unchecked envy. A little envy can be useful if it drives us to better our situation but often it can be problematic and lead to greed and also to following paths that aren't good for us. That's the key factor that most people ignore when dealing with this, the other variable in the situation - other people.
Let's say that you go into work and someone in your team has a beautiful shiny new ferrari. They have been saving for months and months and they just want to tell you all about and how great it is. You listen intently but start to get annoyed, you wish it was you with the new car. You wish it was you with that proud smile. This is because you are only seeing the present, the other person's happiness, the fact they get to drive home in it tonight. What you don't see is how long they probably had to save, what they had to go without, what they will have to do to keep it running and well maintained. It also might not bring you the same happiness it is bringing them. Your situation is different after all. Ironically it's a danger of only living in the present and not thinking about the future or the past.
Another key place that I see this type of thinking (and I suffer from this sometimes as well, much to my frustration) is when people are dealing with their careers and creative pursuits. They want that promotion, that bigger fanbase, that perfect sound. They see an artist playing a style of music and want to go home and start doing that as well as their own stuff. The problem is that this can lead to following hundreds of different paths when a lot of them aren't necessarily even correct or compatible with the life the person has chosen for themselves. None of the paths are bad, but they doesn't make them right either. What if that artists dedicates 8 hours a day to doing just that style? What if the person getting promoted is working 3 hours every night after work because they really love the job? What if you aren't prepared to do that or would even be capable of it? Well maybe then it's worth considering what path is your correct path, rather than what path you would like to have right now. The question isn't "Would I like to have that?", it's "How much work would I prepared to put in to get to that point and keep going?" and also "What would I have to give up to get that?".
I'm not Steve Jobs biggest fan, that's for sure, but there is an old interview where he talks about Apple's strengths and brings up one point about this area. I'm not saying he's some guru or source of wisdom but there is always a danger in ignoring everything someone says just because you don't agree with the vast majority of their outlooks, so i'm including it here. He states that Apple's biggest strength was their ability to decide which things to pursue and which things to ignore, even if they were good opportunities. I think that's key, it's not about the easy things to say no to, everyone can do those. It's about having the discipline to say that some things aren't for you, so you can work on the things you really want, which are right for you and knowing how to recognise those things.