[…] lying alone, he did not know the Somali proverb that says a brave man is always frightened three times by a lion; when he first sees his track, when he first hears him roar and when he first confronts him. (2.11)
The night before the hunt, Macomber already felt deep fear about the lion. Perhaps he would have been comforted to know that everyone who hunted lion experienced such anticipation – or perhaps not. Either way, it does not end well.
Robert Wilson came up then carrying his short, ugly, shockingly big-bored .505 Gibbs and grinning. (2.58)
Wilson fears nothing. For every bit of mortification Macomber feels about hunting, Robert feels pleasure. We can't help thinking that Hemingway would be proud.
"I'll keep you backed up. As a matter of fact, you know, perhaps you'd better not go. It might be much better. Why don't you go over and join the Memsahib while I just get it over with?" (2.121)
I got this, dude. Wilson lets Macomber know that he will finish the job. This backup is a source of comfort and humiliation to Macomber, which definitely leaves him with something to prove.