It's not that economists are always wrong. Now, the ones in the media really tend to be...

1) Politicians: They are more concerned with looking nice to the people in the present rather than being right. For a politician it's far more important to be liked by the people than being right so they say what they perceive as the public's wishes when they speak. When the realization that they were wrong comes, many water already passed under the bridge and they can spin it in multiple ways.

2) Academics: Those who have always lived and worked in the pure academic environment and have no experience in the real world, those who have never worked in positions where their income depends on their accuracy, also tend to be wrong. Reality is far more complex than the sterile academic conditions are able to replicate.

Then you have several others, regretfully very rarely seen in the media anywhere, who work in positions where their expert opinions are important and people's money along with their own depends on what they say, write and do. These are worth listening. Also the ones who have an impressive resumé of earnings due to their efforts, mostly in the financial markets, are worth listening. Consistently earning money in the financial markets throughout a period of several years is the ultimate test about one's understanding of the economy for the way markets move is the sum of all forces acting upon it. Only those who truly understand them can earn money consistently and, therefore, understand the economy and have the ability to look forward to the future.

It's not that economy is like astrology. Far from that. One just must look for the answers in the right places instead of feeding on what those either with an agenda or inexperienced in real world conditions (or both!) say, not in order to enlighten the public but to promote their interests. Don't expect accurate previsions to the third decimal point. Economy is not engineering. From those who indeed know what they are doing, you can expect, however, a very high degree of accuracy and also the presentation of different possibilities according to this or that scenarios occurring in the future. Also these tend to be much less dogmatic than the former.