(Namabyouhou wa ookega no moto; “Green soldiering leads to great harm”)
To do things with an incomplete or half-baked set of knowledge or skills is to invite failure. “A little learning is a dangerous thing; drink deep.” Going into battle with so-so fighting skills is liable to just get you hurt, and the same principle extends to other fields of endeavor.
We begin with nominal prefix 生 (nama), “raw,” or by extension “inexperienced.” This is attached to, gives an initial voicing to, and modifies 兵法 (hyouhou), literally “soldier law” but more generally referring to strategy, tactics, or other martial arts. This entire noun phrase is marked as the topic of discussion by the particle は (wa).
The comment on this topic is another noun phrase, although one can imagine an elided copula. We begin with nominal prefix 大 (oo), “large,” attached to and modifying the noun 怪我 (kega), “injury.” This is followed by the noun 基 (moto), “origin” or “source.” The latter is attached to the former by possessive particle の (no).
Moto may also be written as 元 or 本, or phonetically as もと, or replaced with synonym 疵 (kizu), . But be careful; it’s considered an error to pronounce 兵 as hei despite that being its most common reading in other contexts.
This phrase comes to us from a 16th-century kanazoushi text called the 清水物語 (Kiyomizu monogatari, “A Tale of Kiyomizu [Temple]”).
(“Seken wo senjou da to katei shitara, namabyouhou wa ookega no moto dakara, seken ni hajimete deru toki wa aru shu no youjinbou mo hitsuyou darou.”)
[“If you liken the public sphere to a battlefield, and given that a rookie in battle is asking to get hurt, I’d say that when you first venture into the public sphere you need some kind of social bodyguard.”]