Ces deux mots me semblent avoir le même sens (to lose). Comment sait-on quand utiliser égarer et quand utiliser perdre?
J'ai perdu mes clés.
J'ai égaré mes clés.
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The difference you make in your answer is a subtlety that is not totally foreign to the compared meanings of those two words but not entirely exact. Before getting to that let's see about something else; one difference in the use of the two words is on the count of currency: "perdre" is the word used in the spoken language; the other one is used rather rarely that way and is found in writing but less than "perdre". That shows that French people do not use the two words strictly according to the difference you perceive but that they often say "perdre" when they could have said "égarer"; the reason is that the meaning of "perdre" covers in great part that of "égarer".
The meaning of égarer: Mettre (quelque chose) en un endroit qu'on oublie et où on ne peut (le) retrouver par la suite; perdre momentanément.
Your supposition concerning "égarer" is true as regards a greater chance of finding what has been lost because, as you say, you lost it in a well known and relatively small place (in an office, on the front yard lawn, etc.); that idea contained in "perdre momentanément" corresponds to the use of the word only when you do find what you had lost. If you use the word according to this idea you say "J'avais égaré mes clés" (but now I've got them back), whereas in the other case (considered next) you say "J'ai égaré mes clés.) (You haven't found them yet, and possibly you never will).
The second possibility (Mettre (quelque chose) en un endroit qu'on oublie et où on ne peut (le) retrouver par la suite) shows that what has been lost might never be found again (for instance in the case of keys that fell into a dustbin in the office and were thus lost forever).
The points to stress in acknowledging a difference in the use of "égarer":
the reason for loosing something is inattention while manipulating the object,
you know well the place and it is a small place that you can search,
there is a fair chance of getting back what you lost.
In English the translation of "égarer" is normally "to mislay".
A/ Ce Ngram illustre probablement que le verbe égarer n'est pas courant.
B/ "Égarer" n'a pas tout à fait le même sens que "perdre". "Perdre" c'est : "égarer définitivement". "J'ai perdu ma montre cet été sur la plage". "Égarer" est moins fort, c'est "ne pas retrouver quelque chose" mais cette perte peut être momentanée.