If there is one bid that is almost universally misunderstood and misused by experienced players, it's the conventional bid that shows two unbid five card suits, represented by Michaels and the Unusual No Trump. Michaels is a cue bid of openers' one level bid to show either both majors if the opening bid is a minor or the other major and an undesignated minor if the opening bid is a major. The Unusual No Trump is a conventional bid of a jump to two no trump over an opening one level bid that shows either both minors or the two lower unbid suits.
The problem arises because these players have heard from some "expert" that some people play these only with "good-bad" hands and with intermediate range hands they bid the two suits individually. There are two problems with this statement.
The first is that the "expert" never defines what a "bad" hand is. They tell you that the intermediate range is probably 10-16 HCP, but don't define a range for the "bad" hand. As a result, the "expert's" trusting acolyte defines bad as anything under 10 HCP.
The second is that it defies reason. Why would you want to force your partner to bid at the three level (in the case of unusual no trump) when you have a weak hand and she might be forced to bid a two card suit (or in rare circumstances a one card suit)?
This happened to me recently in a two table social team game. Here's my hand:
The bidding went:
West North East South (me)
1D 2D 3C Dbl
3D P P Dbl
P P P
I'm salivating. We're going to kill this hand. My partner has the majors and I have the minors. At a minimum, I should get three tricks, two diamonds and a club and my partner should have at least two quick tricks to make her bid. Well, to make a long painful story mercifully short, we were the ones who got killed. My partner had four points, one queen and two jacks, and couldn't take a trick. I got my three tricks, but that meant they made their bid with an overtrick, doubled.
When the round was over, the player at the other table who had my partner's hand, a more experienced player than my partner, said that she bid it the same way. Since her partner was not an expert, the final diamond contract wasn't doubled (one of the reasons experts do well is that they love to double partscores).
The reason they both bid Michaels? Because they had heard that it should be used with "good and bad" hands. Well, they certainly had a "bad" hand. But because the "expert" never defines the "bad" hand, people think that any 13 cards that are 5-5 in shape will suffice.
So, clearly, people don't understand this dichotomy and it's time to explain it. First, it makes no sense to only use it with good or bad hands and to bid intermediate hands by bidding the suit. Second, if you use these conventions, use them all the time in accordance with the following rules:
For Unusual No Trump:
Not Vulnerable: At least 5-5 in your two suits, not less than 9 HCP and two quick tricks in your suits, and if at the bottom of your range, you must have good suits. You may have any upper range of points, but this is the minimum.
Vulnerable: At least 5-5 in your two suits, two quick tricks, and generally, not less than 12 HCP; if both of your suits are good, however, you may do it with 11 HCP.
Not vulnerable. At least 5-5 in your two suits and 8 HCP with the points all in your suits, if making the bid with the minimum.
Vulnerable. At least 5-5 in your two suits and 10 useful HCP, meaning at least two quick tricks, and they should be in your suits.
Let me explain why discipline is important. First, often when you have a two suited hand, your partner holds the other two suits, so you might find yourself in a defensive position where you can double for penalty, as I was. You must ensure that your partner can trust your bid and vice-versa.
Second, since you are forcing your partner to bid at a higher level with unknown shape and values, you are risking a bad contract that might be doubled, so you must have the values promised above.