How random is random?

[Rhaegar]

Don't want to spoil any quest info here, so I'll try to keep it brief and simple enough to let people who know what this is about to get what I'm getting at, without ruining the fun for those who don't.

So, today I came across a certain black book in this one big mansion. The book contained a spell of conjuration.
I remember that in my past life, when I was but stupid, young goblin without any knowledge of magic, I managed to cast the spell with my first try.
Now, that I'm a smart elf, skilled in the ways of conjuration, I fruitlessly tried to cast it, without any success until my whole mana was gone...

Any hints on how does this work? What am I missing here? Is it just bad luck?

[Earth]

Keep trying...I had one old character that took over 35 times to finally cast that right.

[Chanele]

I think it require a certain skill

[Rhynox]

When you fail so often, it is because you are missing something. Some races like dwarves have problems casting spells because of low intelect, wisdom and spellcasting skills. Some like ogres can't cast some at all.