The first answer to this is that you could just pick whichever makes most sense to you. For instance, most German authors treat the Anchor as a card of work, while the French more often use the Moon card.
Another answer is that you could see different aspects of these things in each card. The Anchor is traditionally about the hope of salvation through work (for the German protestants with their work ethic). It could also be seen as something that weighs you down, but where you have a choice to lift anchor and move on if you so choose. The Moon could be your reputation, which is certainly relevant to most people's job. And the Fox can be about skills you need for work, or about someone at work with independent skills, such as a contractor or entrepreneur.
However, in this instance someone raised the objection that they could see the sense in several options. They had decided to see how it came out in readings, but were finding it confusing, as it seemed to vary.
My personal take is that the cards are always multivalent: they can potentially indicate several things, and may be read differently when combined with different cards, or using a different technique within the same spread, such as knighting compared to reading diagonals.
While in tarot this multivalency is often connected with what you actually "see" in the image, a little detail perhaps jumping out at you, in Lenormand cards this is more about the spectrum of keywords associated with a card.
There are different levels of interpretation that can be applied to any card. Thus, the Lily can be an older man (connected to the King of Clubs playing card association), or it can signify harmony and peace, or elders, or sexuality and even purity (lilies used to be given at weddings), or some might say death (another situation where lilies are used).
While this may seem confusing, it's also true that life is rarely simple and clear-cut. For instance, a relationship could be quite tumultous, with lots of arguments (Whips/Birch Rods), yet also with lots of make-up sex (also Whips/Birch Rods).
|Letter, Birch Rods, Lord|
If you want to try for a simple answer, just look for one card either side of the card you're asking about, as I did here with the Birch Rods. A simple interpretation would be to journal (Letter) about the card and find the logical (Lord) pattern.
Other interpretations are possible, though. While journalling about the card (Letter) is one interpretation, another is that you can simply take the card at face value (Letter can be associated with superficiality), or look for tangible evidence one way or another, which would take you back to journalling your readings.
Looking to the Lord, he could say "Make a decision and stick to it, no matter what!" Another interpretation, though, might be to "look to the man". Both the Birch Rods and the Lily are associated with male playing cards: the Jack of Clubs and the King of Clubs. I would see the Jack as more youthful, sexual energy, and I tend to prefer interpreting Birch Rods for sex. However, if it was an affair with an older man...
As with the Anchor, Moon and Fox, some people see different aspects of sexuality in the Birch Rods and the Lily. Lily tends to be treated as more "vanilla", if that is relevant to your querent. And as I say, I'd see Birch Rods as "break-up" or "make-up" sex, while I'd associate the Lily with sacred sexuality.
The bottom line, for me, is that life is complex. So, while you can certainly choose an association and stick to it, you may well miss a lot of subtleties that way.