When formulating lay precepts based on his distinction between skillful and unskillful, the Buddha never made any allowances for ifs, ands, or buts. When you promise yourself to abstain from killing or stealing, the power of the promise lies in its universality. You won’t break your promise to yourself under any conditions at all.
(Thanissaro Bhikku, “Getting the Message”, accesstoinsight.org)
The difficulty in this point of view is that skillful means is not something that is acquired through willful action, whether that action is for good or not. Keeping the precepts willfully, in the belief that one is taking the high road and acquiring skill, will result in ill- there’s a passage in the Pali suttas where Gautama talks about “what we will, what we intend to do, or that wherewith we are occupied” and explicitly states that regardless of whether such action is for merit or demerit, ill will result. I would say that skill along the lines that Gautama spoke of is acquired through the experience of absorption in one’s own nature, not otherwise, and that this experience begins with the freedom of the sense of place and the contribution of an ability to feel “with no part left out” to the movement of breath. The disciples of Gautama were described as like wild beasts, and the person making the description considered that a good thing.
“(33) Again you have heard that it was said to those of old, ‘You shall not swear falsely, but shall perform to the Lord what you have sworn.’ (34) But I say to you, Do not take an oath at all, either by heaven, for it is the throne of God, (35) or by the earth, for it is his footstool, or by Jerusalem, for it is the city of the great King. (36) And do not take an oath by your head, for you cannot make one hair white or black. (37) Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil.”
There are those who say the precepts are the gateway of Zen, and it’s true that Gautama said “making self-surrender the object of thought, one lays hold of concentration, one lays hold of single-pointedness of mind.” Self-surrender as the object of thought is a kind of precept, and the word Zen is derived from the Sanskrit word “dhyana”, which means concentration, so at least in this sense something like a precept may in fact be considered a gateway to concentration. Nevertheless, the induction of states characterized by “single-pointedness” of mind is like falling asleep- it’s not done through the exercise of will- and the benefit of such states, like the benefit of sleep, is in well-being, out of which sound action arises.