Are you born with acting ability or can it be learned. It has to be a skill that is naturally in the person before the training will do any good. Most actors can sing and dance as well. These skills are just born in the person but do require a little nurturing to be a valid skill. 
The actors that have little natural talent have little chance of making a living as an actor. The demand is low and the applicants are many. Producers can be very picky when seeking to fill a role. Jobst recently said that acting is a born in ability and you cant train effectively.