ABYSMAL REALMS HELP FILES

CONCENTRATION

When you lose your concentration while casting a spell, it means that your
skill check didn't succeed.  This is influenced by a few different factors.

The most important factor is your actual skill percent in the spell.  In the
output of prac or spells, the percent is the base chance that the spell will
cast successfully.  75% means that the spell will work, on average, 3 out of
4 times.

Some events have an impact on your effective skill chance.  Being drunk will
lower your skill chances, and the effect is more profound the more drunk you
are.  If you're at maximum drunkenness, you'll hardly be able to get anything
to land!

Being bashed, tripped or otherwise dazed can lower your skill chance, too.
This is, incidentally, why re-wielded weapons can sometimes be 'clumsy in
your hands' even though you've mastered them.  Being dazed affects all
skills, not just spells.

Note that 'You failed' and 'Spell failed' messages are not the same thing as
loss of concentration!  If you 'fail', that means that your spell did
actually cast, but the enemy has saved against it to some degree.  If you see
'spell failed' while dispelling, that means that you have weakened a spell
that is currently on the enemy.  The more 'spell failed' you see, the closer
you are to successfully dispelling something.