The person who forgets any of his Torah learning: request for clarification

In Avot 3:10 we learn in the name of Rabbi Dostai ben Yannai (citing Rabbi Meir) that a person who deliberately sets out to forget any of his Torah learning is regarded as though he has forfeited his spiritual life.  

Way back in the 1990s I heard a modern commentary on this Mishnah to the effect that it applies where a person possesses -- as most of us now do -- a reasonable set of sefarim from which he can easily and conveniently look up the things he forgets but he chooses not to do so, whether through lethargy or indifference. 

Unfortunately I do not recollect who said this. Can any reader please point me to a source for this explanation?