It's hard to say how long a trend will last. I swore up and down that skinny jeans wouldn't last because they were too closely related to tapered pants. I was very wrong. I also said leggings would go out eventually, and I've been noticing a lot less leggings in stores lately. Thankfully.
According to the American Marketing Association, there's three phases of a trend:
The Emerging phase: When a item is highly sought after.
For example, a handbag straight off the runways.
This tote debuted late 2010/early 2011(?). This bag is such a classic it will last you a lifetime.
It's still highly coveted, and there are still waitlists at the few stores it is sold in.
The Emulation phase: People start wanting in on the trend.
Coach, J.Crew, and other mid-range designers start producing similar designs.
The Steve Madden bag is a bit of a stretch, I'll admit, but if you look at a big picture you can see the design copy.
You know Cosmo, the magazine? It now has it's own cheap and tacky line at JC Penney now
(the green bag on the bottom right hand corner).
The Saturation phase: Trend is everywhere.
Or: Wet Seal and Charlotte Russe have their own versions.
I looked through various websites where the products are under $50, such as Wet Seal, Charlotte Russe,
Forever 21, Target, etc. I didn't find anything close.
According to the AMA, most people buy will buy the item between stages two and three. This time period is key when determining how long a trend will stay. This has become increasing hard due to the introduction of flash fashion from stores like H&M and Forever 21, the latter supposedly being able to get a design in stores in under a week. The Celine bag trend in question still looks to be in phase two, but will be hitting phase three probably towards end of this year/early next year. If it's just now trickling down to Penney's, it's still going to be a bit before tweens can buy it dayglo pink.
In short, the better the quality of the item, the longer you're going to be able to use it. If you're buying things from Wet Seal or Charlotte Russe, it's going to last you maybe 6 months before looking outdated.
