One of the major themes in the novel is the lack of emotional maturity that the boys share, as well as their ego-driven desire to be seen as brave by the others. Adding on to this is the fact that Ralph and Jack both want to be the de facto leader of the group, although neither is specifically suited for the task. During Chapter 7, the boys discuss going up the mountain in pursuit of "the beast." Ralph, still trying to be a rational leader, wants to camp for the night, but Jack has been using Ralph's caution against him and is aiming to undermine Ralph's authority.
"I'm going up the mountain." The words came from Jack viciously, as though they were a curse. He looked at Ralph, his thin body tensed, his spear held as if he threatened him.
"I'm going up the mountain to look for the beast-now." Then the supreme sting, the casual, bitter, word. "Coming?"
"I don't mind."
Astonished, he heard his voice come out, cool and casual, so that the bitterness of Jack’s taunt fell powerless.
(Golding, Lord of the Flies, staff.bcc.edu)
Jack is using psychology to make Ralph seem weak in front of the other boys. Ralph, feeling his power and his influence slipping away, feels he has no choice but to rise to every occasion, especially if Jack seems willing to do things while Ralph refuses. It is this ego-driven impulse that causes Ralph to be more foolhardy, as otherwise it would appear that Jack is more brave. Without that drive, and with the ability to inform the boys rationally, Ralph may have resisted the urge to out-perform Jack, and become a better leader.