If you have a desire to something you would like to do or have at a given time, but the realization of such remains impossible by many uncontrollable factors (like the weather/budget/…), you become often detached from this desire, and rest your mind about it. You might compromise to something else and be happy with it.
However, when someone puts your attention to the original unfulfilled desire: “Why don’t you do this now, this is a good opportunity, you should really do it”, the desire will grow stronger and the resistance against the less controllable conditions will become stronger.
This desire will temporarily become acute, and sadness or anger might be the result.
As an example, when I was a 10 y.o. boy, I really wanted to get a Slot Car Racing Set for Christmas. But 40 years ago the price was the same as it is still today, so my parents bought me a compromise car set that was not electro-powered and could take my ordinary matchbox cars.
I was quite happy with it until my neighbour friend came to play and shouted: “Why couldn’t you get the real thing!” This made me sad and unhappy for a couple of days.