The Dunning-Kruger effect is usually associated with people over-estimating their own abilities, but the researchers also found that competent people may under-estimate their abilities. Taken to the extreme, this is called the imposter syndrome, where perfectly competent people feel that they are imposters at their jobs.
There are those that question the generalizations involved in the Dunning Kruger effect. I take this as a good reminder not to rely too heavily on particular studies. The following article suggests we are all rather poor at estimating our own abilities.
Whether the Dunning Kruger effect is real or not, I stand by my suggestion that a writer look for external evidence to make judgments about having enough skill and knowledge to contribute rather than dilute.