When to bemoan and when to moan

I've tried looking this up and I've read somewhat unhelpful advice like "to bemoan something is to moan about something".

I am mostly aware when one feels correct, and when one does not, but I'm not sure why.

I bemoaned my fate.

I moaned every day and night for the last month.

I moaned my fate.* (wrong)

I bemoaned every day and night for the last month.* (wrong)

(Taken from this related question)

Solution 1:

"Bemoan" is a transitive verb which takes an object so you can "Bemoan your fate" but not just "Bemoan" in the abstract or "Bemoan about your fate".

"Moan", however, as an intransitive verb which does not take a direct object so you can't "Moan your fate" but you can "Moan" in the abstract or "Moan about your fate".

Solution 2:

As suggested in the following extract bemoan is a transitive verb whose object is generally an abstract concept (absence, lack, failure etc.) while moan is an intransitive verb:

Bemoan is one of a group of English verbs starting be-, where the effect of the prefix is to turn an intransitive verb into a transitive one. So to wail is to cry out in pain or sorrow, while to bewail something is to complain strongly about it. Bemoan fits with this pattern:

to moan is to complain, and to bemoan something is to complain about it. The ‘something’ is important: typical objects of the verb are nouns like ‘lack’, ‘dearth‘, ‘absence’, ‘decline’, ‘failure’ and ‘loss’, along with ‘fact’.

You do not usually bemoan people, yet the other day I saw someone hoping she would not turn into ‘a decrepit old woman bemoaning young people with their whole lives in front of them’. The writer seemed to be using bemoan to mean ‘moan at’ or even ‘nag’, rather than ‘complain about’. I haven’t yet seen this meaning used widely, but it will be interesting to see if it catches on.

(macmillandictionaryblog.com)

Solution 3:

Besides the already mentioned transitive/intransitive difference, another difference is that the word moan is usually associated with making an audible noise, whereas this is not the case with bemoan.

For example, Merriam-Webster mentions audible noises in both verb definitions of moan, but not at all for bemoan.