underpredictor
underestimator
underthinker
underreactor
overpredictor
misguider
overexplainer
undervaluer
misdealer
misunderstander
overstimulator
overstayer
overstater
undersaver
underdeliverer
undeceiver
misconstruer
misapplier
misperceiver
overestimator
underinvestor
undervoter
overspender
overstepper
overthinker
underreporter
misaligner
misdescriber
misjudger
disinformant
disinformer
discreditor
overreactor
overresponder
misinformer
contradicter
underspender
obviator
underuser
mislabeler
misconceiver
mismanager
subexpert
rulebreaker
Grundyist
underreader
misstater
miseducator
misteacher
Monday-morning quarterback