[fnurt]

What MLG means is, you want to guesstimate that he has, let's say, a 30% chance of a pair and a 70% chance of overcards, and figure out where you stand in both instances. This kind of composite calculation gives you a more accurate result.

To illustrate, let's say that for some reason, you know the guy must have either AA or AK, no other hand. There are 12 ways to make AA, and 32 ways to make AK, so the chance that he holds AA is 12/44.

If you were to say to yourself, "AK is his most common holding, so I'll put him on that hand," rather than including the possibility of AA as well, you'd be making a serious mistake.