Well, it's not that you can guess there is a reflexive form. But I suppose that once you know there is, it's pretty easy to get the meanings of each. I speak Portuguese, and althought it's very very similar, some reflexive verbs in Spanish are not reflexive in Portuguese.
The only context I can think of (thanks to your reply) within which 'I lost.' or 'He lost.' is OK as a sentence is playing a game, as in 'I lost (the game)!' Is that what you are thinking of, rmcgwn? Which then means that perdi or perdio can be used to mean lost in the context of losing a game?
Hi Linda, I'm on my phone so I don't know when you asked this question, but I will answer anyway. In your sentence, the main verb is "to be" (estar) and lost is being used as an adverb. A translation would be "él estuve perdido".
I hope I've made that about as clear as mud! (or at least dirty water)
Sometimes I'm frustrated by the number of unanswered questions in these discussions. Three years ago dholman asked if "perdir" could mean to lose (a game). One year ago Tin-Naz wanted to know the same. There's still no answer to that question. I feel like DuoLingo leaves us poor students to wander aimlessly through the learning experience.
I feel your frustration. Unfortunately, the comments section is not an area to interact with staff to get questions answered. It is simply a place for students to help one another. Duolingo simply does not offer an interactive learning experience. Ultimately it's best use is for practice drills and picking up new vocabulary. Here are some free resources I use in tandem with DL to guide my learning:
http://www.spanishdict.com/dictionary (Be sure to check out the tabs like "conjugation" and "examples". Also notice that many of the bold words are links that will take you to explanations of other things such as moods and tenses. It even includes the reflexive versions on the same page as the "regular". It's a lot more than a dictionary.)
https://www.thoughtco.com/spanish-4133085 (This is not the most intuitive site to navigate for me. However, the articles on it go into great detail on a variety of topics and have helped me to understand some of the more complicated topics.)
And yes, perder can mean to lose (a game). http://www.spanishdict.com/translate/perder
In this case, we have a pronoun marked Él (he). Since the subject is explicitly stated we know the sentence must focus on "he." Predió supports this too, since we are using the 3rd person singular ending -ió.
In the previous examples we did not know who was performing the action. Comió for example. It could be "she ate", "he ate", or "it ate".
I am not quite sure I fully understood the question that was asked, but I hope this helped some.