Jack is excited about becoming a hunter. He will attract a group of followers to become hunters with him. One of the problems that will emerge is that Jack and his followers do not pay enough attention to building shelters and they neglect the fire which is their primary means of being rescued.
Jack is ambitious about becoming the lead hunter because it suits his personality. He wants to be a (young) man of action and wants to appear as a strong, fearless leader. However, his first attempts at hunting reveal his fear and apprehension. He hasn't yet acquired the skills and fearlessness that he needs to actually go through with killing the animal. At the end of Chapter 1, the pig escapes because Jack is scared, apprehensive, unsure, or all of the above.
The three boys rushed forward and Jack drew his knife again with a flourish. He raised his arm in the air. There came a pause, a hiatus, the pig continued to scream and the creepers to jerk, and the blade continued to flash at the end of a bony arm. The pause was only long enough for them to understand what an enormity the downward stroke would be. Then the piglet tore loose from the creepers and scurried into the undergrowth.
Jack's hesitation allows the pig to escape. The other boys recognize that Jack is scared and Jack takes offense to this, saying "Next time--!" Jack then sets his mind on developing a killer instinct.