Theory:

     At length we did get the thing into position; and the moment it was in position he burst out laughing.
 
     I said, “What’s the joke?”
 
     He said, “Well, I am an ass!”
 
     It was the first thing he had said that made me respect him. I asked him what had led him to the discovery.
 
     He said, “We’ve forgotten the balls!”.
 
     I looked for my hat; it was lying topsy-turvy in the middle of the path.
 
     He was of a cheerful disposition. He said, “Well, we must put back all we can find, and trust to providence.”
Explanation:
 
Finally, after a lot of effort, they managed to hold the wheel in the desired position.
 
The moment the wheel was in position, the man burst out laughing. The narrator couldn't figure out the joke in the situation and asked him why he was laughing.
 
The man responds by calling himself an ass. The narrator couldn't agree more. He felt that it was the only sensible thing uttered by him since his arrival. He asked him what had made him say so.
 
It so happened that the men had forgotten all about the little balls. They are supposed to fix the wheel using those balls. The narrator quickly looked for his hat, for he had left the ball bearings in it for safekeeping. Unfortunately, he had dropped his hat (along with the balls) while he was trying to position the wheel.
 
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The man laughed because he forgot about all the balls
 
In the end, the man suggested in a cheerful manner that they should put back the balls they could find and leave the rest to the fate.
 
Meanings of difficult words from the paragraphs:
 
Sl. No.
Words
Meanings
1
AssFoolish person
2
Topsy-turvyIn utter confusion or disorder
3
DispositionA person's inherent qualities of mind and character
4
Providence
Fate
Reference:
National Council of Educational Research and Training (2007). Honeycomb. A Bicycle in Good Repair (pp. 126-132). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.