I can't get the wording exactly right on this question, and it's gonna take some explaining. Nephi says this about the Lord's commandment to get the brass plates,
"for I know that the Lord giveth no commandments unto the children of men, save he shall prepare a way for them that they may accomplish the thing which he commandeth them." (1 Nephi 3:7)
Later, when trying to keep the commandment to get the brass plates, he and his brothers failed twice, but he said,
"As the Lord liveth, and as we live, we will not go down unto our father in the wilderness until we have accomplished the thing which the Lord hath commanded us. Wherefore, let us be faithful in keeping the commandments of the Lord;" (1 Nephi 3:15-16)
Later he says,
"And it came to pass that thus far I and my father had kept the commandments wherewith the Lord had commanded us." (1 Nephi 5:20)
His last words in the Book of Mormon are,
"For what I seal on earth, shall be brought against you at the judgment bar; for thus hath the Lord commanded me, and I must obey. Amen."
It seems clear to me that every commandment can be obeyed. But it's very hard, especially to obey constantly. I'd like to know why was he able to do it? I believe at the root of that is the question: Why did he believe he could do it rather than believing he would eventually fail? The obvious answer is that it isn't his own strength, but the grace of God that makes this possible, but what makes the enabling power of the Atonement available constantly rather than "every so often"? I'm not sure how to believe that obeying the commandments is really truly all the time possible, and I think I'm misunderstanding the doctrine of grace.