Harlan sits next to 4 phonetic neighbors — Harlen, Harley, and Carlan are the closest matches by sound. Most share Harlan's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"rocky land, stony ground"
"courageous heart"
"defender of men"
"peace, complete"
"clay settlement, clay worker"
"possibly from a- (not) + treo (tremble)"
"God's peace, divine peace"
"true, faithful"
"born on Sunday"
"from the settlement by the stone"
"watchful, vigilant (via Casey influence)"
"wolf lover"
"beloved"
"river that swallows all rivers"
"son of Walter"
"Brixis settlement"
"dragon"
"from the western settlement"
"warrior"
"the cleansing one"
"young lion"
Similar sound: These names share phonetic patterns with Harlan — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Old English origins, giving them the same cultural heritage as Harlan.
Rhythm: Harlan is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.