出る杭は打たれる (Deru kui wa utareru; “The post that sticks out gets hammered down.”)
It is best to keep one’s head down and not attract too much attention. Someone whose ability stands out will become the target of others’ jealousy. Someone who is full of themselves will be humbled by the censure of their peers. Depending on your point of view and the specifics of the situation, this can be negative (a bitter, even Randian comment about how the mediocre will attempt to drag down their betters) or positive (a warning against hubris in a world where even those who see the farthest do so only because they stand on the shoulders of giants).
The verb 出る is literally “to go out,” and is incredibly common in Japanese, in a wide variety of uses and combinations. In this case, context allows us to understand that it is being used to mean “stick out,” since presumably the 杭 in question are not mobile, nor are they being launched through the air. The verb is acting adjectivally, modifying the noun 杭, “stake,” “post,” etc. は is, as usual, the topic-marker particle, but we can see a hint of its contrastive use here: the post that sticks out, as opposed to all the other posts, gets hammered, and they do not. Finally, the verb 打つ, “to strike,” in its passive form. Rendered literally, the phrase becomes “As for out-going post, struck.”
出る can be expanded into 差し出る (sashideru), which more explicitly indicates “sticking out” or “jutting out.” 杭 can be replaced with 釘 (kugi, “nail”), although the former seems to be the original term.
The origins of this kotowaza remain unclear to me, although there seems to be a general consensus that the posts in question are involved in rice agriculture, perhaps marking the boundaries of fields. I believe I read once that the expression comes from as far back as the Chinese Water Margin epic, but please don’t take my word for it without further research.
(“Hm. Deru kui wa utareru to iu kara, shibaraku damatte mawari no hito no iken wo kiite miyou.”)
[“Hm. Since ‘the post that sticks out gets hammered down,’ let’s be quiet for a while and listen to the opinions of the people around us.”]