fathom
v.to understand something difficult or strange after thinking about it for a long time. You often use it in the negative when you find a situation impossible to explain.
v.to penetrate to the truth of something; to comprehend a difficult or obscure concept. Frequently used in negative constructions to indicate a total lack of understanding.
“I cannot fathom why he decided to quit his job.”
“After hours of debate, the committee still could not fathom the logic behind the CEO's sudden strategy shift.”
“The sheer scale of the universe is something the human mind struggles to fathom, as our daily experiences occur on a vastly different physical dimension.”
The verb is transitive and takes a direct object, often a 'why' or 'how' clause.
Fathom already means 'to understand'; adding 'to understand' after it is redundant.
“People can’t fathom that the Dark Personality is dark, they can’t believe that anyone would want to be deliberately harmful, they can’t process that harm was caused at all.”
“That AI could not fathom the experience of being unable to hear isn’t surprising.”
From Middle English fathome, fadom, fadme (“unit of length of about six feet; depth of six feet for nautical soundings; (loosely) cubit; ell”) [and other forms], from Old English fæþm, fæþme (“encircling or outstretched arms, bosom, embrace; envelopment; control, grasp, power; fathom (unit of measurement); cubit”) [and other forms], from Proto-West Germanic faþm (“outstretched arms, embrace; fathom (unit of measurement)”), from Proto-Germanic faþmaz (“outstretched arms, embrace; fathom (unit of measurement)”), from Proto-Indo-European pet-, peth₂- (“to spread out; to fly”). Cognates * Ancient Greek πέταλος (pétalos, “broad; flat”), πετᾰ́ννῡμῐ (petắnnūmĭ, “to open; to spread out; to be dispersed or scattered”) (whence English petal) * Gothic 𐍆𐌰𐌸𐌰 (faþa, “fench; hedge”) * Latin pateō (“to extend, increase; to be accessible, attainable, open; to be exposed, vulnerable”) * Low German fadem, faem (“cubit; thread”) * Middle Dutch vadem (modern Dutch vaam, vadem (“fathom”)) * Norwegian Bokmål favn (“an embrace; a fathom”) * Old Frisian fethm (“outstretched arms”) * Old High German fadam, fadum (“cubit”) (Middle High German vade (“enclosure”), vadem, vaden, modern German Faden (“fathom; filament, thread”)) * Old Norse faþmr (Danish favn (“an embrace; a fathom”), Icelandic faðmur (“an embrace”), Swedish famn (“the arms, bosom; an embrace”)) * Old Welsh etem (“thread”)
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.