two_sum compare for loop & while loop

Compare for loop and while loop in two sum problem, I wonder why in case of while loop needs to be len(s)-1 for the code to work as the arrow pointed out?? Do we not need to get to the last element of len(s) ??? def two_sum(s, target):

for i in range(len(s)):
for j in range(i+1, len(s)):
if s[i]+s[j]==target:
print(s[i], s[j])
return True
return False ____________________________________________________ def to_sum(s, target):
 i=0
 j=len(s)-1 <------------------why ???
  while i <=j:
 if s[i]+s[j] ==target:
    print(s[i], s[j])
    print(s.index(s[i]), s.index(s[j]))
  return True
 elif s[i]+s[j] <target:
 i+=1
 else: j-=1
return False
print(to_sum(s, target))