My answer is simple; politics is making a decision for the tradeoff between now and the future.
To begin with, why should politicians exist? Today, we can present our own opinion quite easily with internet. Theoretically, direct democracy like Poleis in the ancient Greek era can be realized with modern technology. We can determine all things around our lives with decision by majority.
However, this political state will no longer maintain. The reason is human bias.
We tend to attach greater importance to immediate pleasure than fruit in future. We cannot ignore our own interests. In individual decision, we can often be patient. But in total, human are egoistic. Therefore the decision of the majority is likely to be short-sighted. It is so called as populism.
To elect a politician by voting is to concentrate our thought into one person. He has enough time to learn about the complicated issues. He will be supervised by citizens, not to be concerned about his own interest too much. And his decision may be more radical than the total will of the people.
A politician must have a tough time, occasionally being hated by the citizens. Cost cutting is hardly achieved under the influence of populism. In the contrast, complete satisfaction of all citizens sometimes means to force the next generations in the future to pay sacrifice.
There is always a tradeoff between the present prosperity and happiness in the future. I think making a balance of this dilemma is the ultimate work performed by politicians.
Unfortunately, most politicians set their purposes as to being politicians. Before the next election, they cannot make any decision to sacrifice citizens before them.
In Japan some politician decided to raise taxes up. After all they lost a lot of seats in the next election without exception. Raising tax might be inevitable to maintain the government. Nonetheless, citizens exiled the policy makers with voting. It is a great dilemma of modern democracy.