Hebrews 10:26 isn’t talking about ordinary sins like lying, pride, lust, or anger. The context of Hebrews shows that the willful sin in view is rejecting Christ and His once for all sacrifice
Throughout the entire book, the author repeatedly emphasizes the superiority of Jesus and warns Jewish believers not to turn back to the old covenant system. That’s why he says, “if we go on sinning deliberately after receiving the knowledge of the truth, there no longer remains a sacrifice for sins.”
What is “the knowledge of the truth”? Paul in Ephesians 1:13 identifies it as the gospel
“In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit.”
If someone rejects the gospel after hearing it, there’s no other sacrifice available for their sins. The blood of bulls and goats could never take away sins. Only Jesus can. To reject Him is to reject the only sacrifice God has provided