Use 'fitful' when something occurs in unpredictable bursts rather than consistently. His concentration was fitful, waning every few minutes.
Pro Tip 2/3
Negative Nuance
'Fitful' often implies discomfort or instability regarding the situation being described. The baby's fitful cries worried the new parents.
Pro Tip 3/3
Not for Positives
It's unusual to use 'fitful' with positive events; it typically describes disturbances or interruptions. The artist's career was marked by a fitful success, with long periods of obscurity.