Suppose, hypothetically of course, that you're a very good, Uruguayan, professional football player. Having amazing skills would be pretty pointless if you keep getting suspended because nobody told you that it was against the rules to bite the occasional defender. Of course, it's unlikely that anybody would be this naive in reality, but it supports the notion that gaps in your understanding of the basics of something can ruin your overall performance. As Chuck Noll once said:
“Before you can win a game, you have to not lose it.”
With this in mind, I wanted to quickly run thought weaknesses with ICM. There should be little doubt that a comprehensive understanding of ICM will help your game, but using ICM is not without flaw. Yes ICM can calculate the financial value of your current chip stack, but because it's near impossible to accurately quantify the edge a player has over his opponents, it does so on the basis that every player is of an equal ability, which is rarely the case. The start of a tournament is a good example of the kind of issues this presents. Here's how a $20 SNG might look (let's ignore the rake):
As you can see, ICM suggests that because the stacks are equal at the start of a tournament, everyone's stacks are worth the same. However, if you have a skill advantage over your opponents, your stack is more valuable than theirs as you're going to win this tournament more often than your opponents in the long term. In this case, ICM is undervaluing your stack and overestimating the value of stacks of the players you have the edge over.
Make sure you play with this in mind and remember that if you do feel that you have a decent edge over your opponents, it is completely fine to pass up on a spot that ICM says is profitable if you think you can push more profitable, lower variance edges.
Another issue with ICM surrounds stack expression. Most of us are accustomed to expressing our stack in terms of big blinds, and you may have noticed that that the size of the blinds has never been considered when we've made any ICM calculations. ICM is calculated using your percentage of the total chips in play, and just as it ignores skill advantage, it disregards the size and fluctuation of the blinds.
This means that an ICM calculator may encourage you to do something like shoving in a spot where logic might suggest that folding is better. A good example might be on a 9 max hyper turbo bubble with an unusually shallow average stack of 3 big blinds. Let's say you're on the button with 3bigs, and the blinds double next hand forcing both blinds all. Your ICM calculator, unable to consider this dynamic, might recommend you move all in here when folding to almost certainly guarantee yourself a min cash next hand may well be the best play.
Additionally, ICM based shove/fold calculators are hindered by the accuracy of the ranges you are assigning to your opponents. If you believe an opponent is folding more hands than they actually are, you would be overestimating your fold equity and you'd probably be shoving too wide as a consequence. This might be the case when someone is tilting (which we can't always be aware of) and can cost you a bunch of money.
In fact, ICM is unable to take any meta-game considerations into account. Is a player is drunk, mass multi-tabling, or is there someone sitting out on the blinds? Keep an eye out for these kinds of things because anything that can have an impact upon your opponents' ranges should affect your decisions proportionately. Minimise the impact this has by studying your opponents as best you can, and make sure that the ranges you are entering into you calculators are adjusted for each villain and their current position.
Remember, ICM is like Durex, it's only effective if used correctly, the trick is to use it alongside your own logic and make your decisions from there. If we are using ICM correctly we will have a huge edge over opponents that are not, especially during the shove/fold stages of a tournament, where a good understanding of ICM is paramount. As ever, if you have any questions, feel free to send me a message or leave me a comment in the forums.
Gl felt side, danshreddies.