Most of us would disagree with
@cj428mach , as would most of the buying public, or we'd all be on a Falcon forum instead of a Mustang one. Don't get me all wrong, I love the Falcons too, but they were boxier, more utilitarian, as well as dated and copied by GM and Mopar in the early to mid 60s so Ford needed something to set their new car apart from -ahem- the herd.
And
@Master Hack has some good points here as well, but looking at the evolution of the design of the Mustang, as with any other car, from radical "SEMA concept" or online renderings we see now, of course these people knew what they were doing, but it was a process not unlike any other that thankfully yielded results that were
not like any other.
It was the right car, at the right time, at the right price - for almost anyone - from the single on the make and just starting out, the departing or returning service person, the family needing a second car, the weekend or professional racer, the accomplished businessman with new disposable income, the socialite that needed to be needed. $2500 to $4500 got you to work and back, out on the town and back, or to the track and back.
What made and still makes a Mustang timeless?
It's because it's damn near universal.
The car made to be made by you.
We all have a story to tell.
The car takes us there.