Pro 1:17 Surely in vain the net is spread in the sight of any bird.
Pro 1:18 And they lay wait for their own blood; they lurk privily for their own lives.
Pro 1:19 So are the ways of every one that is greedy of gain; which taketh away the life of the owners thereof.
This parable may be seen as a continuation of the previous one, or perhaps as a separate parable. The "they" in verse 17 is still the wicked. The format of this parable, however, is to show the foolishness of the wicked.
The "net" mentioned is a snare net used to catch birds in the era before shotguns. The point of verse 17 is to simply point out that if you set a trap for a bird while the bird is watching, it is not going to do any good. It's pointless or vain to waste your time on such an activity.
This foolishness is then compared to the even greater foolishness of the wicked. They are described as ambushing themselves. Not only do they know of the net that they are about to be snared in, they themselves set in place! This is the sort of activity that makes the Dodo look brilliant.
Notice how poetic paralleling is again used to reinforce the point of what it is that the wicked are doing:
they lay wait for || they lurk privily for
their own blood || their own lives.
Both laying wait for, and lurking privily for are descriptions of an ambush, and both "their own blood" and "their own lives" indicates murderous intent. They are their own assassins.
The parable concludes by identifying the wicked people mentioned. These are people who are "greedy of gain." In general, these are people who have avarice: they desire material wealth that is not already theirs, and this is their driving force. It's a suicidal urge.
We know that it is a suicidal urge, because of the way that the parable concludes: "which taketh away the life of the owners thereof." Material wealth can be like a poison. One doesn't normally see headlines like, "Man killed by wealth," and yet that is the effect that wealth can have on man.
In reading this verse in English, it seems like the verse may be speaking of people who are so greedy for gain, they kill people in order to get wealthy. This would go well with the idea that the previous parable and this parable are all one parable. Nevertheless, it seems that this is not what is intended, but instead the connection is to gain itself (את - eth) taking away the life of its owner.
In any event, the warning is clear: it is foolishness to listen to the call of avarice and greedily seek after wealth. A bird has the sense to avoid a trap that it sees being set for it, so also a man should have the sense to see that his quest for wealth is a trap for his own soul.
17 כי־חנם מזרה הרשׁת בעיני כל־בעל כנף׃
18 והם לדמם יארבו יצפנו לנפשׁתם׃
19 כן ארחות כל־בצע בצע את־נפשׁ בעליו יקח׃
17οὐ γὰρ ἀδίκως ἐκτείνεται δίκτυα πτερωτοῖς. 18αὐτοὶ γὰρ οἱ φόνου μετέχοντες θησαυρίζουσιν ἑαυτοῖς κακά, ἡ δὲ καταστροφὴ ἀνδρῶν παρανόμων κακή. 19αὗται αἱ ὁδοί εἰσιν πάντων τῶν συντελούντων τὰ ἄνομα· τῇ γὰρ ἀσεβείᾳ τὴν ἑαυτῶν ψυχὴν ἀφαιροῦνται.
17frustra autem iacitur rete ante oculos pinnatorum 18ipsique contra sanguinem suum insidiantur et moliuntur fraudes contra animas suas 19sic semitae omnis avari animas possidentium rapiunt