So you cast your spell, and now you are waiting for it to work. But what happens if days go by - or weeks - and nothing happens? What happens if you think your spell failed to work? Do you recast it? Do you continue waiting? What should you do?
I think that you should continue waiting and not recast the spell. Now, this belief is going to differ from person to person and faith to faith. Let me explain why I believe you do not need to recast your spell.
It is taking its time.
I believe that, if you did not set adequate parameters for the energy you cast out during your magickal working, the spell will take its time and manifest when it feels like it. Now, this could mean that it takes months for the spell to work the way you want it to. It could be that you did the spell this way on purpose. I know for some of my magickal work, when I have asked for the assistance of the Gods, I left it in Their hands to decide when the time was right for me to receive what I wanted. If this is the case, be patient and know that They might know better than you. If you did not do your spell this way, maybe you just forgot to set parameters for the energy in your spell. That happens, and it is okay. But still, be patient and wait it out for at least six months before you consider recasting. And I will tell you why in a minute.
It is not the right time.
This goes along with the example of my magickal work when I ask the Gods for their assistance. Maybe I am being greedy. Maybe the Goddess that I am giving an offering to in exchange for their help sees a better opportunity for me. Or - and this does happen - They do not want to help, so the spell takes longer or does not happen at all. Depending on your beliefs, this could be a valid reason why your spell is taking longer than you want to manifest. If you asked for help, consider that.
Something went wrong.
Again, this goes back to parameters and how you cast your spell. If you do not focus properly or you do not give the energy any direction or instruction, your spell will fail. Maybe you were trying to make a honey jar but instead of sugar, you accidentally used salt. Sugar is a key ingredient in any sweetening jar spell, so using salt instead will either not work or have the wrong effect. Consider this spell, in this case, a learning experience. Maybe you need to learn more about correspondences and ingredients before trying again.
Your heart isn’t in it.
This might be harder to pin down, but if your heart or your subconscious does not really want the thing you are asking for, your subconscious might redirect the energy unbeknownst to your conscious mind. Your spell will not work in this case because the energy you were directing received conflicting intentions and, therefore, did not know what to do.
You are asking for the impossible.
Now, I know some things appear impossible but, in reality, are well within the laws of physics or our physical world. However, if you begin to ask to breathe underwater, throw fireballs, or - less conspicuously - literally change the color of your eyes, you will be sorely disappointed. Magick will not allow you to go above the laws of physics, no matter how much you want to.
So, should you cast that spell again? Maybe. Maybe not. While you attempt to answer that question, keep these points in mind.
Have you ever had a spell fail more than once? Or have you ever felt the need to cast a spell again? Let me know!
I really like the concept of setting the adequate parameters for raising energy. Set and Setting are crucial in my opinion.
or a journal of some sort to go back and see what you did, when you did it, what ingredients you used, etc.
I saw your comment on another post about your sweetening jar possibly failing. I’m sorry to hear that! I hope it becomes more clear over the course of time 
Having a limit isn’t a bad thing and it doesn’t devalue magic in the slightest, in my opinion.