Good Question.
There are 4 billion patterns in chess. No 2 chess games are ever similar just like no 2 trading days are ever similar.
In cricket, an international batsmen has no idea where bowler is going to bowl. Still the top batsmen manage to score runs. Did your uncle said chess or cricket is gambling?
The unknown part in trading which novice traders refer to gambling is the part which needs to be managed after proper training and practice.
Trading is a zero sum game. The 2% consistent winners takes all the money 98% looser offer. In poker also, the winning rate is only 2%.
Hence, the 2% consistent winners are grand winners since they digest all the money which 98% looser offers. This is the reason that someone who is successful in reading the market will end up making quite a lot of money over a period of time.
The success in trading comes through lot of hard work, practice and memorization of patterns which is known as COGNITIVE LOAD. You are feeding your brain through a structured training practice just like in any other profession.
The easy way out is to draw geometrical lines on charts or calculate fibs/pivots or those magical support and resistance. These easy ways may work sometimes but will never work consistently.
Trading just like any other profession needs tremendous training. The challenge is you need to figure out the chaos all your self.
The successful 2% traders don't come on TV or don't sell their services/calls. With practice, they have developed a great ability to read the market, manage the unknowns and extract the profit from the market.
Some one who goes through few hundred/thousand hours of structured training will start reading the market correctly and he/she deserves the monetary reward.
It is interesting to note the monetary reward of a winning trader is coming from the looser. One happiness is another sorrow. But that's how the system works not only in trading but in every other profession.
The grinding hard work, frustrations, disappointments, managing the unknown (which your uncle is referring to gambling), even some loosing trades will see the survival of the fittest which is around 2% and they will take all of it in the worlds most rewarding profession which is trading.