How does Ralph lack self-confidence in Lord of the Flies?

Ralph lacks self-confidence with his hesitancy to assert the values that he initially represents.

When Ralph first blows the conch and the boys assemble, they afford Ralph respect because he looks like a leader; for, he is the handsome golden boy. Ralph encourages the boys to build a rescue fire and maintain it at all times, and he urges them to build shelters from storms. But, somehow, Ralph does not possess the forcefulness to ensure that tasks are completed. 

Further, as the group gradually yields to their savage instincts, Ralph’s position declines while Jack’s rises. And because Ralph possesses some of these savage instincts himself--he is gratuitously cruel to Piggy in the beginning, for instance--he participates in some activities and finds himself in a quandary, at times.
In Chapter Eight, for instance, he stands on the platform and reiterates the importance of the fire:

"Without the fire we can't be rescued. I'd like to put on war-paint and be a savage. But we must keep the fire burning."

However, he is ineffective in keeping the boys directed toward doing what they should, especially as Jack gains power. For instance, in Chapter Nine, Ralph again urges the boys to keep up the fire. He accuses them of running after food, instead. Interrupting him, Jack accuses Ralph of running himself. When Ralph says he has the conch, Jack derisively tells him, "You haven't got it with you...And the conch doesn't count at this end of the island--"
As the boys run with Jack, Piggy warns Ralph that there is going to be trouble.
Then, it is not long before Simon comes down from the mountain to tell them that there is no visible beast. Ignoring Simon in their ritual frenzy, the boys perform their hunting dance, and this time they beat Simon who wants to tell them what he knows about evil. Sadly, they kill him before he can explain that there is no visible beast. Moreover, Ralph and Piggy have been on the outer ring of this dance when Simon dies.

Ralph's participation in the rituals of the evening have short-sighted him, also, but the next day he confronts the truth. Piggy tries to excuse their participation by saying that they were frightened although Ralph scolds him, "Don't you understand, Piggy? The things we did--"
At this point Ralph's self-confidence is gone as the memory of the dance "that none of them had attended" shook him and Piggy. After this tragic knowledge, Ralph, who has lost his confidence, must simply try to survive against the savagery to which the others have descended since chaos and anarchy reign over the island.