use it or lose it
it's not what you know but who you know
rude
a little knowledge is a dangerous thing
slow
dim
dense
dull
dumb
obtuse
skill
clueless
rusty
weak
bungling
fumbling
incompetent
clumsy
muddle through
unfamiliarity
subexpert
nativism
pons asinorum
untalentedness
underbrained
unskillfulness
untempered
incognizance
fixed mindset
hard skill
out of practice
the cobbler always wears the worst shoes
nonsavvy
stupid
nonverbal intelligence
not the sharpest tool in the box
layman
not yet
find out the hard way
skill issue
ignorant
unlearned
nescient
not the sharpest knife in the drawer
not the sharpest tool in the shed
unlettered
darkness
unintelligence
slow on the uptake
obtuseness
dullness
underskilled
unknowing
unknowledge
knowledgelessness
unintelligent
unwitting
slow study
unknowledgeable
backward
ineffective
shallow
new
unskilled
unaware
lackluster
obscurity
reconditeness
obscureness
abstruseness
incognizant
something
inscient
shallow end
pall
you're only as good as your last shift
forgotten
outskilled
ineptitude
vocational
vacancy
clumsiness
indocible
lose one's touch
bad
ineptness
ham-fisted
more haste, less speed
inexpert
slowness
another string to one's bow
maladroitness
skillessness
awkwardness
retard