I do agree that every professional actor needs to undergo acting classes because it can train them how to do their jobs right. But if you are going to dig deeper, the truth is and actor is only as good as his memories. They need to remember anything that happened in the past so they can relate themselves to the character. No amount of internalization can make any good actor project emotions he hasn't experienced yet. Funny, the greatest actors are actually the "greatest actors" because they are good in pretending they are okay.