What does Mark 14:8 mean?

Although Jesus often wanted His identity as Messiah to be kept quiet (Mark 8:27–30), He never kept secret that the Jewish leadership would kill Him and He would rise again (Mark 8:31; 9:31; 10:32–34; Matthew 26:2). The disciples understand on some level (John 11:16) but not completely (Mark 9:32). This shortcoming is partly because it isn't time (Luke 18:34). Had they truly understood, they may have tried to prevent it (Mark 8:32–33).

Jesus often warns His followers to count the cost of following Him (Matthew 8:18–22; Mark 8:34–38; Luke 14:25–33). The Twelve are more interested in what they can gain (Mark 9:33–38; 10:35–41). Mary of Bethany considers worldly losses or gains nonsense compared to the spiritual treasure of having Jesus (Philippians 3:8). Some time before, she ignored the honor and obligation for hospitality to merely sit at Jesus' feet and listen to Him (Luke 10:38–42). Four days ago, she, too, dedicated a valuable flask of ointment and anointed Jesus' feet (John 12:1–8).

Now, either Mary again, or another woman, has anointed Jesus' head, on the same night Jewish families are making preparations for their Passover lambs. It's entirely possible that the Holy Spirit is prompting Mary and this woman to honor and worship Jesus in this way without their full understanding. But it's also possible they do so intentionally because they understand Jesus is about to die.