Source: http://www.vba.asn.au
You hold your usual hand: 
J53 
632 
J864 
Q105
No one is vulnerable, LHO is the dealer, and passes, then your partner opens 2NT, showing a balanced hand and 20-22 HCP.
Next hand passes. Simple arithmetic tells you that your combined assets are 24-26 HCP, so you may or may not have enough strength to make 3NT. Should you bid it?
Here’s this month’s tip:
[box]Hands do not play well when one-sided in strength[/box]
In other words, a very strong hand opposite a very weak hand has problems in the declarer play.
The reason is that the very weak hand lacks entries: there will be problems of communications. This has two effects: first, you might be able to establish winners in the weak hand, but will you have an entry to take them? And second, there might be a finesse you want to take through RHO, but will you have the necessary entry to try it?
The bottom line is: 12 opposite 12 is a lot better than 20 opposite 4!
So in the example problem, I would pass 2NT and hope partner makes it. The hand will probably be difficult to play.
Conversely let’s boost the hand a little: J53 632 AJ86 Q105
We’ve added an ace, to bring it up to 8 HCP; the rest of the hand is identical. This time, your LHO opens 2, a weak two, and partner overcalls 2NT, showing 16-18 HCP.
The maths is identical: your side has a combined total of 24-26 HCP. But this time, it’s worth bidding 3NT. There’s a far better chance of being able to establish and cash winners in your diamond suit. And there is a cast-iron entry to dummy, which may be helpful if partner wants to take a finesse, for example through the hearts of the weak-two opener.