How to buy a blazer that will never go out of style

Gentlemen, we know what you want.
You want to buy an item of clothing and have to never buy it
again. You want to buy something timeless.
In that spirit, we're going to start teaching you how to identify
the classics.
We'll start with a piece of clothing every man needs to have in
his closet — a blazer.
A few things before we go point by point.
 The classic blazer
is navy in wool or cashmere, with high-contrast buttons (think
gold or silver).
It is not a sport coat, which is less formal and usually in a
tweed or some other pattern. Historically, blazers were used
for sailing and tailored closer to the body, while sport coats
were used for hunting and were cut more loosely.
Now that you have the context, for tips on how to buy a blazer
that will always look fresh, we turned to stylist Jessica
Cadmus of the Wardrobe Whisperer.
"There's a lot of emphasis on gender fluidity in fashion right
now," Cadmus said, "but despite the fusion of women's and
men's clothing, every woman I know still likes to see a man in
structured, traditionally masculine garments like blazers.
Experimentation with fashion is great, but stock your closet
with the basics. To quote the Dalai Lama, 'Know the rules well
so you can break them effectively.'"
The tips:
When in doubt, go classic. In terms of color, this means
navy blue. In terms of lapel, go notch. In terms of cut, go
two-button (versus double-breasted or three-button)
Concentrate on fit. The shoulders are critical — the
shoulder seam should not extend beyond the end of your
own shoulder. If you are between two sizes, go with the
smaller. Natural fabrics have inherent "give," which
means that once you begin wearing them, the fibers will
loosen and the garment will "grow" by 1/4 inch to 1/2 inch
and conform to your body
If the torso looks boxy, ask your tailor to shape the body.
Basically you should not be able to fit anything bigger
than a baseball into the chest area when the jacket is
buttoned.
Make sure that 1/4 inch to 1/2 inch of shirt cuff extends
from the cuff of your jacket
Vents are your choice (single or double) but the double
vent is flattering on more body types
Make sure the width of the lapel is moderate in size; too
skinny or two wide will give away the year you bought it.
Similarly, make sure the notch isn't placed too high — it
should more or less line up with the shoulders or slightly
below.
The bottom of your jacket should fall roughly at the same
place as your cuffs when you are standing with your arms
resting at your sides. If you are 6-foot-2 or over, you can
select a jacket that covers more of your backside. If you
are 5-foot-6 or shorter, choose a jacket on the shorter
side. This will extend your form.
It's all about how it fits, people. Make sure it's right, and for
the love of God go see your tailor.