Every good human quality is related to a bad one into which it threatens to pass over; and every bad quality is similarly related to a good one. The reason we so often misunderstand people is that when we first make their acquaintance we mistake their bad qualities for the related good ones, or vice versa: thus a prudent man will seem cowardly, a thrifty one avaricious; or a spendthrift will seem liberal, a boor frank and straightforward, an impudent fellow full of noble self-confidence, and so on.

[Jede menschliche Vollkommenheit ist einem Fehler verwandt, in welchen überzugehn sie droht; jedoch auch, umgekehrt, jeder Fehler, einer Vollkommenheit. Daher beruht der Irrthum, in welchen wir, hinsichtlich eines Menschen, gerathen, oft darauf, daß wir, im Anfang der Bekanntschaft, seine Fehler mit den ihnen verwandten Vollkommenheiten verwechseln, oder auch umgekehrt: da scheint uns dann der Vorsichtige feige, der Sparsame geizig; oder auch der Verschwender liberal, der Grobian gerade und aufrichtig, der Dummdreiste als mit edelem Selbstvertrauen auftretend, u. dgl. m]

Arthur Schopenhauer (1788-1860) German philosopher

Parerga and Paralipomena, Vol. 2, ch. 8 “On Ethics [Zur Ethik],” § 113 (1851) [tr. Hollingdale (1970)]
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(Source (German)). Alternate translation:

Every human perfection is allied to a defect into which it threatens to pass; but it is also true that every defect is allied to a perfection. Hence it is that if, as often happens, we make a mistake about a man, it is because at the beginning of our acquaintance with him we confound his defects with the kinds of perfection to which the are allied. The cautious man seems to us a coward; the economical man, a miser; the spendthrift seems liberal; the rude fellow, downright and sincere; the foolhardy person looks as if he were going to work with a noble self-confidence, and so on in many other case.
[tr. Saunders (1890), "On Human Nature"]

Every human perfection is akin to a fault into which it threatens to pass; conversely, however, every fault is akin to a perfection. And so the error into which we fall in respect of a man is often due to the fact that, at the beginning of our acquaintance, we confuse his faults with the perfections akin to them, or vice versa. The cautious man then seems to us to be cowardly, the thrifty to be avaricious; or again, the spendthrift appears to be liberal, the lout straightforward and sincere, the foolhardy to be endowed with noble self-confidence, and so on.
[tr. Payne (1974)]

Every human perfection is linked to an error which it threatens to turn into.
[Source]