Can caster of illusion opt to believe their own illusion?

Question

Related: Are Illusionists subject to their own illusions?

My character is a Forest Gnome. He is afraid of blood, so I want him to cast Minor Illusion to create cloth covering the blood of his opponent (after he is killed) when trying to search his pocket. I can't search his pocket because my PC would see the blood and become frightened. But, if I can cover it with cloth, he won't see the blood when searching his pocket.

Because we are allowed to voluntarily fail saving throw, is it logical to convince my DM to allow my PC to see the cloth as opaque, and not faint?

If a creature discerns the illusion for what it is, the illusion becomes faint to the creature.

Note: I know Minor Illusion does not involve saving throw, but it's similar, I think.

Answer 1

Possibly, but it would be complicated

As has been said above, no rule allows you to voluntarily fail a saving throw. However, (as you mentioned) since the Minor Illusion spell has no saving throw, that's not a problem here.

Also, as you mentioned, the only thing that causes an illusion to become faint is "if a creature discerns the illusion for what it is, the illusion becomes faint to the creature." So the only way your illusion could stay solid for you after you cast the spell is if you do not know it is an illusion.

There is one thing working in your favor here: the spell Minor Illusion does not need to be cast in an area you can see (although, like most spells, it cannot be cast through total cover). As such, you could close your eyes, and say something like "Hey, everyone in the party: if you can find a green cloth, please silently put it on top of the blood" then cast the spell. If you open your eyes and see a green cloth over the blood, your DM might rule that you are not sure if that cloth is your illusion, or a real one put down by the party (lying on top of your illusion).

If you were to cast the spell while looking in that direction, and saw the cloth pop into existence, you'd definitely know you were looking at your illusion (since you cast the spell yourself: there is no question where it came from). A DM might also rule that the above trick doesn't work, since the cloth you see will me in the exact arrangement (crumpled where you thought it would be, with the exact color of green you thought it would be) that you imagined while casting the spell. But it is within the realm of possibility.

Personally, I'd recommend just searching with your eyes closed, or cover the view of the blood with your hand close to your face.

Answer 2

Belief isn't an option, you need to erase the knowledge

Try to believe that the sun won't come up tomorrow. Try to believe that when you jump off a building gravity won't pull you to the Earth and break you.

Beliefs are not optional. Knowledge informs belief, so unless you had a way to make your caster forget they cast the illusion in the first place, there's no way for the caster to disbelieve their own illusion. This is the only caveat to it. If somebody used Wish or some other memory augmenting spell on your caster to forget the illusion was created, then your caster would not by default know that it was an illusion and believe it to be real.

Answer 3

What does belief have to do with it?

Your PC knows the cloth is an illusion. So what? The magic still deceives his senses into seeing it. Knowing a mirage is a mirage doesn’t make you stop seeing it.

As for physical interaction; the spell description says the illusion goes faint. Faint means “hardly perceptible”. This in not necessarily translucent: could still be opaque and serve the purpose you want. Work with your DM.