What is its etymology? (And, no, it's not from "blog" - blogs aren't exactly the source of self-restraint.)
In his entry, Klein writes:
Base of uncertain origin and meaning: usually rendered by 'to restrain oneself'. Most scholars connect it with Arab. balija ( = he gleamed, smiled), however, the verb הבליג could hardly have this meaning in the verses in which it occurs in the Bible.
However, in the verses themselves, it didn't mean "restraint" either. The Targum consistently translates הבליג as גבר, and Kaddari writes that it means to overcome someone else. The classical commentaries also explain הבליג as "becoming stronger".
It is beyond the scope of this blog to explain the Jewish concept of heroism, but we see also with the root גבר that it can mean both to "become strong" and "to overcome (oneself)".
An interesting source in Shabbat 77b is both related to this root and to today's situation. The gemara lists a number of cases where small animals can scare larger ones, and the proof of this is the pasuk from Amos 5:9 - הַמַּבְלִיג שֹׁד, עַל-עָז "Who sends forth destruction against the strong".
So after all this, our conception of havlaga and who is strong and who is weak is more confused then ever. Maybe my next entry will have more clarity...