Faith of a Mustard Seed or The Dunning-Kruger Effect

In 1995, a man named McArthur Wheeler walked into two banks in Pittsburgh and robbed them in broad daylight. He wasn’t wearing a mask. He wasn’t in disguise. His “master plan” was to smear lemon juice on his face, believing it would make him invisible to security cameras because lemon juice can be used as invisible ink. He was quickly arrested, confused at how he was caught.

Psychologists David Dunning and Justin Kruger read about this case and began studying why people so ignorant of a subject could be so confident. Their conclusion became known as the Dunning–Kruger Effect—a cognitive bias where those with little knowledge overestimate their ability, while those with real depth often underestimate themselves.

This odd story mirrors something in our Christian walk.

Faith That Grows or Faith That Assumes

Jesus told us that faith as small as a mustard seed can move mountains (Matthew 17:20). But that mustard seed must be planted, watered, and cultivated. Faith that doesn’t grow roots can become presumptuous—mistaking excitement for depth, or charisma for calling. That’s where the Dunning–Kruger effect sneaks in: when believers assume they’re equipped for spiritual battles, leadership roles, or theological debates without truly being grounded.

Testing Knowledge, Building Depth

The Bereans in Acts 17 were praised because they didn’t just accept what Paul said—they examined the Scriptures daily to see if it was true. In the same way, testing our knowledge in prayer, study, and community keeps our confidence from outrunning our competence. Faith without this discipline becomes reckless, like Wheeler with his lemon juice plan—full of confidence, but heading for disaster.

When You’re Not the One for the Job

In ministry, not every open role is yours to fill. Being passionate doesn’t equal being prepared. Being talented doesn’t equal being called. Moses had Aaron, David had prophets to counsel him, and even the apostles appointed deacons to serve so they wouldn’t neglect the Word (Acts 6). Knowing you’re “not the one” in a specific role is not failure—it’s wisdom.

The Antidote: Humility and Growth

The true cure to the Dunning–Kruger trap in Christianity is humility. A mustard seed of faith grows not because of its size but because it surrenders to God’s process. Likewise, knowledge matures when we accept correction, remain teachable, and stay rooted in Scripture.

Action Steps for the Believer

1. Check your foundation – Are your convictions rooted in Scripture or just in feelings and trends?


2. Stay teachable – Seek discipleship, mentorship, and correction without defensiveness.


3. Test your faith – Allow trials, study, and service to refine what you believe.


4. Know your lane – Ask God honestly where He has called you to serve, and respect roles He hasn’t.


5. Cultivate humility – Pray for a spirit that admits what it doesn’t know and leans on God’s wisdom.



A little faith can move mountains, but only if it is surrendered to God and cultivated with humility. Anything less risks turning us into lemon-juice believers—confident, but blind to the truth.