The phrase "key culprit" means the main or most important cause or person responsible for a problem or negative outcome.
Sentences with «key culprit»
The back - to - back findings come amid a stream of evidence pointing to genetic rearrangements as key culprits in autism. (scientificamerican.com)
Stress, anxiety or depression are often key culprits of thyroid dysfunction. (fullhealthsecrets.com)
The biggest obstacles to this are: habit, the usual key culprit; the allocation of valuable time («If I take time for this, I may not get to the Civil War by Christmas!») (edutopia.org)