memfido

Mem at rank 90 is self, the emphatic one: mi mem means I myself. Fido is trust, the noun built on fidi at rank 750. Put them together and you get trust in oneself, which is self-confidence, and the word costs you nothing to learn because you already own both halves. This is what the affix and compounding system is for, and after twenty-five chapters of it the machinery should be starting to feel automatic.

Mem- against sin-, which is the real lesson here. Esperanto has two ways of saying self at the front of a compound and they are not interchangeable.

Sin is the reflexive pronoun in the accusative, so a sin- compound names something the subject does to itself, with the pronoun as the grammatical object. Sinteno at rank 1828 is a self-holding, which is your bearing or your attitude. Sinsekvo at rank 2344 is a following-of-itself, a sequence. Sindona is self-giving, devoted. Sinmortigo is suicide. In every one of them you can turn the compound back into a clause with a verb and an object: teni sin, sekvi sin, doni sin.

Mem- is the emphatic self, not an object of anything. It says the thing happens by itself or of itself. Memstara at rank 2343 is self-standing, standing unaided. Memlerninto is a self-taught person. Memfarita is homemade. Memfido belongs here: you are not doing trusting to yourself as an object, you have trust that is your own.

The test is the clause. If verbi sin makes sense, use sin-. If it does not, and what you mean is "by its own means", use mem-. Get it wrong and you will still be understood, but a fluent reader will hear the seam.

Neighbours. Memfido is confidence in your own abilities. Memestimo is self-esteem, what you think you are worth, which is a different quantity and frequently moves in the opposite direction. Aroganteco is arrogance, the failure mode. And fidi on its own takes al or a direct object: mi fidas vin or mi fidas al vi, I trust you. Manki in the third example is the verb Esperanto uses where English uses lack, and it inverts the sentence: what is missing is the subject, and the person who is short of it takes al.