Desire is one of the strongest emotions a person can have. It is one of the main driving forces of magick.
You say that this thing you want is impossible to get. Without knowing just what it is that you desire, I can't give you a definite answer, but I can tell you that I have learned that very few things in life are actually impossible.
If you want something bad enough, you will usually find a way to get it. The question becomes, is that thing really what you wanted, or is it simply a manifestation of a deeper desire?
A person could desire to win the lottery. The chances of winning are a few hundred million to one, but it is certainly possible.
But the real desire isn't winning the lottery, it's having enough money that money is no longer an issue.
Once you see the actual desire, and understand it for what it is, you start to realize there are other ways to fulfill it.
You could start a business selling a product or service. If that product or service is something people want, they will gladly give you money for it, and you could end up having more money than you can spend.
It's not winning the lottery, but the outcome is effectively the same. You get the money you desire.
If you desire a particular person, is it the particular person you desire, or do you really want someone who can make you feel loved?
We tend to think in terms of particular people, especially when we are young. What we come to discover is that particular people who attract us in a specific way (usually physical) may not be able to satisfy us in other, more important ways.
They may not be able to give us the emotional support we really desire, and even though we are in a relationship with them, we are not happy.
You must think very carefully about what it is that you truly desire, then start looking for that.
Remember, be careful what you ask for, you may just get it. Then you may find that it isn't what you really wanted.