because you miss out on the enormous amount of chips you pick up by stealing the antes/blinds….you also give your opponent the chance to outflop you, and you also can't afford to lose chips ever with under 10bb.  There are countless reasons as to why limping is terrible, but if he doesn't open his mind to switch his style of play he is pretty much saying he won't learn anything and won't get better.

Guppy has it right – he can't outplay his opponent on the flop because he's not a threat.  One standard raise/re-raise and he's pot committed.  Worst case scenario for opponent is losing 9 more BB. No real threat.  The hands I might fold against

A bigger stack can easily widen his starting hand versus your buddy because of effective size (10BB) and take a shot at knocking him out.  Your friend's limp is twofold – a.) Hope he is not repopped and b.) hit the flop.  He is just looking to get lucky for a BB (Spent and probably won).  The odds of both of those happening are not in his favor (Around 30% – or over 2 to 1).  You want to try to get those 10BB into at least a coinflip situation if you can and push it all in.  He is throwing money away twice to make it work once  –  funny it never really works out that way though. 

The time for speculation hands passeed him a long time ago – he has two moves and you know what they are.

Another consideration, especially final table – his limp is inviting other players into the pot.  Let's say four other guys jump in on this limp – most of them (or all)just looking to knock him out of there and one BB is not 10 percent of their stack so they decide to gang up on him.  Even if he has AA – his limp put him in the position of his monster hand being only 56% to win – whereas a shove versus a single opponent he would be 85%.  He just cut his winning percentage by 30% to limp.  What does he do on the flop, turn, river?  Since the objective of the other guys is to knock him out he is going to have reveal his hand sooner or later.  He checks and is going to be shocked to see everyone else check behind.  You think that turn card could help one of these four guys with maybe a set?  Trips?  Straight?  Flush? A big draw?  He is just continuing to screw himself by refusing to shove his stack so he can outplay people.

He has got to find the faith and courage that, unlike the forward pass in football, there are three outcomes and two of them are good.  He either picks up the blinds, doubles his stack or is sent packing.  Grow a pair and go for it.

I'm sure Guppy found it so ridiculous he couldn't even begin to articulate reasons and that's why his post is so short