M

It's a term invented by Paul Magriel and received the most press in Harrington's 2nd book. It represents the ratio between your stack and the blinds/antes. Harrington wrote a whole guideline on what to do with certain ranges so beginners no longer have to put any thought into their games.

Morphy

Ouch. Not a fan of Harrington - or beginners? I use M as a guide to what to do, not as the be-all end-all of decision making.

However, as a beginner, maybe I just don't get it. Maybe I should stop

It explains a lot of Xaq's play, that's for sure.

With all the emphasis on M, Harrington on Grammar (aka bad book editing 101) takes all thinking away from players. They are so worried about calculating M every 3 seconds that they miss most things going on around them.

Morphy

You could say the same about most concepts in books. Some people focus too much on starting hand requirements and don't properly adjust to their table or when the table gets shorthanded. Some people worry too much about how much to open for and not about who they're playing against. M is just one way to think about where you are at in a tournament. I think it's more useful for understanding your opponents' moves in relation to their stack size than as a guideline to say that if you're in the yellow zone, you can push with Q8 suited or whatever.