Question: I've started Wing Chun few days before. Everything seems to be nice, but I've seen some videos on internet, they say that Wing Chun can't handle Boxers or Wrestlers.

What are the comparisons between Wing Chun and boxing/wrestling that would lead someone to make this claim? Are there weaknesses that can be exploited?

Answer: 
The great advantage of boxing and wrestling is that boxers and wrestlers practice actual fighting, with all other elements of their training - weights, bag work, jumping rope - in support of improving them as fighters. Even when practicing a constrained format a boxer's conditioning, strength and (most importantly) familiarity with hard contact will invariably see them roll over the top of more esoteric fighting methods. Regardless of the style, the single greatest determinant of effectiveness is hard, realistic sparring. If you want to learn how to fight, practice fighting. It's a no brainer
So there are some fundamental assumptions here that one must look at with "intent or goal".

**Goal:
To beat your opponent senseless?**

* If this is your goal then you will probably want a style that focuses aggression and subjugation of your opponent over anything else.

**Goal:
To protect oneself?**

* If this is the goal then any discipline which focuses on body mechanics as well as properly analyzing a situation and working to diffuse it works well.

**Goal:
To develop oneself through discipline and mastery of ones body?**

* If this is the goal then the ability to "beat someone" isn't really as important as the type of person you become through the exercise and mastery of the art. Boxing, Wrestling, Kung Fu, Tai Chi, Karate, etc... all have the ability to develop ones physical and mental techniques while disciplining and harnessing ones own inner self for personal growth.

P.S. Unless you are practicing just for a MMA full contact event, then any style has use, purpose, and value. The only caveat to add is if you are grappling it's hard to hit and if you are at a distance it's hard to grapple, so there is a body mechanics balance needed to be well rounded.

P.P.S. As far as ability to beat another opponent, this is largely circumspect on the individual's abilities and if one is better skilled and physically capable then they will likely win regardless of the style in question.