But I really like this saying, so I'll try to explain what it means in my view:
A cynic is a "non-believer" according to the online dictionary Thesaurus.com. I see a cynic as wearing a protective armour of doubt and pessimism, clad (sometimes, hopefully) in witticisms, but nevertheless with an exaggerated negative outlook on life.
Now a romantic is his (or her) opposite: this person has an overly optimistic view of persons or events. Everything is seen through rose-tinted glasses, as they say.
My point is - both of them are wrong. The metaphor of wearing tinted glasses (whether in pink or black) is appropriate: it distorts the view into a predisposed, favoured, interpretation. But nothing is so simple in real life. Nothing is all bad or all wonderful.
This thing we call life is a giant mesh of the terrible, the
wonderful, the boring and everything in between. Resorting to simplified templates and trying to squeeze them onto our experiences distances us further from the world rather than brings us into it. It judges the world into a dichotomy of good or bad. All nuances go out the window.
And yes, I think it is quite likely that a disappointed romantic will easily swing to the other end of the emotional spectrum and become a cynic.
This is why I have found Buddhism such a relief: it teaches mindfulness over judging and sorting; presence over distancing; and equanimity over emotional upheavals.
"What IS this?" asks one of my favourite buddhist writers Ezra Bayda when he meditates. What IS this life when we manage to remove our tinted glasses?