문법 구조와 happen to, to make 용법 알려주세요

“Crawling on all fours and groping about in the dark, I managed to get back to the tent after a long, long time.”에서 앞부분의 문법 구조가 궁금해요.
about 뒤에 생략된 부분이 있는지도 알고 싶습니다.
“Because a lad does not happen to be strong, it does not necessarily follow that a sea life would not suit him. A sea life may be the very thing required to make a strong man of him.”에서 happen to와 to make는 각각 어떻게 해석하면 될까요?
도움 부탁드려요.