The desirability of anything depends on a few factors:
1. How useful the object is?
Of course, you will never buy anything that is of no use to you so usability is the number one factor.
2. How much you really want it?
Another important thing is, how much do you want that particular object. For example, there are different kinds of pens available in the market but you might like one better than the other even though it might be more expensive or harder to find.
3. How many other people want it?
The more people that buy a thing, the desirability of it will go up. The general thinking is, if people want it so much, it must be good.
4. Who do you know is using it?
This one is a very unconscious factor, and it is what all advertising is based on. Movie stars and models are brand ambassadors because people buy things because they market it. Silly yes? But then, that’s how it works. Not just celebrities, but also if someone you like uses a product you are likely to use it as well. If someone you don’t like uses something, you will probably think it’s shit without any evaluation of the thing itself.