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"
"river, great water (from Zaire)"
"defender, protector"
"help, helper"
"son of the wealthy guardian"
"beloved companion"
"where roses grow"
"exalted father"
"of the Julian family"
"famous wolf"
"passionate, earnest"
"short form of Wesley or Weston"
"may God protect, holder of the heel"
"son of the marsh dwellers"
"true, faithful, genuine"
"royalty, ruler"
"messenger"
"bold power, chief ruler"
"drawn out of water"
"son of David"
"courageous heart"
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.